I've got a lot of time in the game so here's my view of it.

1. The base game is bland until you hit max level. Then you open incursions, legendary missions weekly missions and other stuff

2. The dlc will get mixed opinions. Underground is an attempt at Diablo III rifts. It plays well just gets boring fast. Survival is fantastic you spawn in with no gear. You gather materials weapons and gear and Have to make your way to the dark zone get anti virals caches and extract. You can play pvp or pve so killing other agents helps gear you. Or finding dead agents in pve.

3. last stand is an equalised pvp every had max stats evens the playing field out not bad really

Missions have multiple difficulties with varying rewards. There are also incursions with even more rewards. There are world bosses outside the dark one and global events.

The dark one is a PVPVE area. Agents can choose to kill you at random. And others will hunt them down. Unfortunately this is where the game has issuesexploits are very often abused in the dz and in the early game cheaters we're very common. It's died down and is being re worked soon.

The game is now on it's 2nd year of dlc all of the new dlc is free 1.8 is expanding the pve map with even more to do.

All that said it's a good game it has it's flaws just like every other game.