Pros:
A good verity of weapons
A good wide selection of cosmetics (weapons skins/ playable characters)
Good boss/ zed designs
Good voice acting
A very wide selection of maps
Updates very frequently with seasonal content

Cons:
Controller users are not able to re-bind their buttons. For example to change your weapon you need to hold (Y = xbox/ Triangle = ps) In a fast pace game thats not really viable.
Lack of bosses could have at least 5 more

There is loot boxes in the game but I think that's a good/bad thing but i'd leave that to you, However it's only cosmetics.

Hey people of steam,
Now I bet you are thinking is Garry's Mod any good? Is it worth it's money? Is it fun to play? And so forth.
Well to give the short answer is yes, well that's if you are into FPS's and don't take them seriously. Also you can create your own map and game type. The game is server based through out other people creating the maps and the servers. The good thing is that you can play with your friends, get points on some servers and just have fun. The bad points are that is you need other games for example Counter Strike and Team Fortress 2. You need those games to get packs which enable you to play them so it's alot more fun. Personally I really enjoy the game, so I would give this game a 4/5.