For everyone wondering if it is worth it to buy Elder Scrolls Online here is a quick review.

If you are a big fan of the Elder Scrolls franchise in general and like MMORPGs the answer is yes.
It is a great combination and you are able to enjoy the big world which contain most parts of the TES Universe as they add more and more regions on the map like the recently added Murkmire.
It has a decent story and a lot of the gameplay elements are based of the story. There are tons of quests and you gain experience and archievments for exploring the world. There will be absolutely no problems in starting even if you have higher-leveled friends because your character stats will scale to a certain degree allowing you to visit every part without problems.

But if you are interested in only either MMOs or Elder Scrolls games there can be some information you could want beforehand.
The game is not 100% lore-friendly. So if you are a hardcore fan of the Elder Scrolls franchise and know every little detail of the lore there could be some parts in the different regions which might seem off to you and some of the lorebooks could be out of order. On the other hand none of the TES games was 100% lore-friendly.
Also the game is still a MMORPG. If you only want to have Skyrim, Oblivion or any other TES but online, you will be dissappointed. You have couple of active skills and the gearing works also different than from the singleplayer games.

For the fully fledged MMO player there are also different rankings and leaderboards for different PVE and PVP rankings.
It's fun to test different set combinations and builds with Meta and off-Meta variations to customize your own playstyle. There are lot of archievments and the housing system is basically there to show off your whole effort. Most houses require certain archievments and high amount of gold in order to purchase them; making them sort of an endgame content. It will take a lot of time to hit the maximum Championpoint-Cap, which is basically a more advanced attributepoint system.
This Championpoint system also acts like an Accountlevel since the maximum Characterlevel is 50 and the maximum Championpoints are 810; but don't worry you will keep leveling up and when the new cap is released you will have even more points to spent. Each time one of your characters hit level 50 they will be in the Championpoint system, displaying your whole account level. Also all characters have a shared banking system where you can easily swap equipment through different characters to try out stuff on other classes and playstyles.
But if you don't like questing and exploring this might be bad news. In order to gain more skill points than the ones from leveling up you will have to complete different questlines and explore the world to gain more. So if you plan to simply grind mobs to max. level (yes this works very well) you will still end up in a situation where you have to do certain quests at some point. Also if you are used to Free-to-Play-Titles there are also bad news for you.
The game releases more content for players willing to buy the new DLCs than 'free' ones to expand the basegame. You won't be left out since couple times a year ESO+ (the subscription system ingame) is free, allowing you to play the DLCs for a limited amount of time even if you don't own them. Also they are sometimes free like the newest Murkmire expansion which is part of the daily rewards for logging into the game.

If you plan to buy Elder Scrolls Online I highly recommend to purchase it with the Summerset Chapter. Regardless the game has a huge amount of content to offer and I personally really enjoy it. As you can see I spent almost 500 hours and I barely have even explored most of the world - speaking from the basegame only. Most DLCs have additional regions, dungeons and other challenges.
Thanks for reading. I hope my review helps your decision.

Well as you can see I played the game for quite some time; Not counting that the Steam-Client itself is buggy af and you're better off with the Nexon client so I switched to it after half a year.
After playing Riders of Icarus for 2 years since the Beta was released I can say: Never a Nexon game again.

The game also had a problem with cheaters since it did not had any mechanics to prevent people from uploading data into the game. It does not has any filter so there were numerous bugs (for example when you had connection problems) like item duplication. So at certain times some people were selling skill modifications for higher damage, no cooldowns, etc.
To prevent that Nexon switched trough different third-party anti cheat software.
The current one is nProtect GameGuard which will prevent many users from even starting the game.
THIS ANTICHEATSOFTWARE DOES NOT WORK AND IS HIGHLY QUESTIONABLE SINCE
- IT WILL BLOCK FUNCTIONS OF DIRECTX AMD THE WINDOWS API
- IT WILL SACN EVERY SINGLE PROCESS ON YOUR PC
- IT WILL FORCE UPDATES AND NEED ADMIN RIGHTS
- IT HIDES THE GAME APPLICATION PROGRESS
- IT MONITORS THE ENTIRE MEMORY RANGE
- IT KEYLOGS KEYBOARD INPUT
- AND CAN TERMINATE OTHER APPLICATIONS.

Game Info:
Well after mentioning some stuff around the game it is time to talk about Icarus itself.
The game was originally a Korean MMO with a Japanese version shortly after.
Afterwards a version for North America and Europe was released by Nexon which is different in some parts to the Asian counterpart.
Game itself was fun in the early days.
An unique system to motivate players to tame and collect all the obtainable mounts and pets in the game combining classical MMO-gameplay with collecting Monsters similar to Pokemon.

Quests and Leveling:
The quest ingame only have two purposes: To level and to do repeatable quests for items.
The level quests are pretty simple: Go to certain position and either collect or kill. Luckily you can accept alot of quests at the same time so you can simply collect a lot of quests while leveling since the side quests will lead in the same area as the mainquest. If you skip quests or dont collect all, including hidden quests or don't have premium service or other EXP Boosts, you will end up extremly underleveled making the questing more difficult. Questing to make new chars or as a new players is incredibly boring since it only purpose is to show you the map and its regions.
Luckily it is fast and with larger questing sessions you can hit max. Level (currently level 60) in 2-7 days.

Account & Character:
Your Characters DO NOT share a storage together and the only way of transfering items is by using the mail system.
Most Items are bound to the character so you have to make sure to collect most daily or event rewards on the MAIN CHAR.

Gameplay:
The game has 7 different classes: Assassin, Ranger, Wizard, Priest, Guardian, Trickster, Dark Magician.
The roles can be taken from the class names since all equipment is class specific so each class is only playable as such.
If you're interested in PVP you will often face a lot of laggs and a Stone-beat-Scissors-system.
It is impossible for a Priest for example to beat an Assassin or a Ranger for example since they will simply get oneshotted.
Otherways an Assassin for example will get bursted down by the Guardian and so on.
You will receive a lot of different Skills during leveling and for the endgame it is expected for you to master all of them especially as a Guardian and Priest.
The game itself wants you to study the mechanics of every boss and will be very punishing for mistakes.
Dungeons runs will be extremly difficult which will result in having good communication skills and learning your class properly. There's also a ranking system in which every player should participate since it gives good rewards.
The gameplay itself therefore is really fun to play except one aspect: TAMING.
The main aspect was on taming but with pure RNG you will never know if you will get what you want. You can spend days/weeks to craft a 'mark' to try a tame on a certain mount... only resulting in failed attempt. Every booster, taming event, taming gear seems wasted since theres no actual chance. Even with 120% Taming chance you will often get a 100% tame fail and sometimes with nothing you will get a 100% tame. By pressing w,a,s,d theres a small minigame for the tame but the result barely influence the tame itself.
For instances you have: Dungeons, Raids and Worldbosses.
Most players will do most instances in 6-Person groups since with 6 people you will have the highest amount of droprate.
Raids are dungeons made for 10 players but in reality theyre completed in 6 person groups or less to maximize the drops since everyone shares the same chest. Worldbosses are the big events where you have to deal a percentage of the boss max health in order to receive anything. With 5% you usally are able to get the big chest with items instead of a tiny amount of gold (accomplished with 1%). A big problem here is GREED. Because of this system most players tend to do stuff solo or in very small groups, leaving newer players or even experienced support classes behind in order to maximize their profit. Guardians and Priests barely get invited to Worldboss-parties but are highly requested for Dungeon Runs, Raids or even buffing people before certain activities. The Assassin is a completely broken unbalanced class having 2 primary weapons with more slots for enchantments since every other class has a primary and secondary weapon (For example: Guardians have primary sword, secondary shield). This is resulting in Assassins to often abandon their Worldboss groups and go for the solo 5% since they can easily put the same numbers as a 3-5 man group without assassin.
This is also only possible cue to a low playerbase but I will explain that later.

Equipment:
Well one of the most important features since you need very good equipment to perfom well in 'Ellora's Spire' (the ranking system is a dungeon with different bosses), but also to perform well in Dungeons and at Worldbosses. Each gear piece has different stat and you always want the current legendary equipment. Theres no variety and only one piece everybody else uses. You want this set only and it has to have perfect stats and maximum enchantments. Stats are classical stats like 'Strength, Constitution, Intelligence, Willpower' BUT the only stats which matter are STRENGTH for melee classes and INTELLIGENCE for ranged ones. Every other stat is useless since you will get 'All stats' in the Enchantments called 'seals'.
Seals are obtained through taming Familiars, leveling them and afterwards sealing them. Unleveled seals are barely ever used since they barely provide any stats. So you want to sit hours afk on your mounts to level them before sealing, or paying gold/elluns for max. level potions or other ways to boost the level of you mounts.
However the game is insanely grindy and not rewarding at all. You can spend weeks/months of doing daily quests in order to get the needed material to craft the newest equipment; only to craft into a low or very low chance and fail, fail and fail again. There no percentages for doing this and the only thing you can see is normal low or very low. Players have theories if normal doesnt actually mean 30% or lower since the Devs are adjusting it from time to time.
And even if you get your piece its not over. You will porbably have to reroll the stats until you get max Strength/intelligence and also temper it. After you reach +10 you need to use Elluns (cash Shop currency) in order to get it higher. If you dont use Elluns to save the step your equipment most likely will go down one or two stages (for example +19 -> +20: if you use elluns and fail you will stay at +19...if you dont lock it...you will go down to +17)
So it will result in an endless grind until you unlocked all; just to realize that the game barely offered any content.