Grim Dawn, the spiritual successor to Titan Quest. You can play the game offline/single player mode. If you want to play GD with your rl friends, you have the option to go in multiplayer, and put it in LAN. Of course, that is just an added bonus.
The game is not done yet, Crate just recently added the faction update which includes bounties and etc. The game might finish this year depending how they go with the updates. B26 will include level cap increase to 45, the last part of act 3, and more. There is still act 4, devotion, and other stuff they will add into game further down the road. After release, Crate will eventually release the mod API (not sure what to call it), so you can mod any part of the game and add more contents.
But yea, I recommend Grim Dawn.