Darkspore

This is a game meant for co-op. Solo can get boring, but 4 player co-op is an enemy-stomping action-packed blast. Luckily, a very straight-forward random matchmaking system makes finding a full group a breeze even when you can't find any friends online. It also has quite a robust reconnect feature so if one of your players drops out mid-mission, he can get back on pretty easily.

The loot system is fantastic. The great pieces of gear you get for level rewards are great at directly stimulating the "phat lewt" center of my brain. The catalyst system is another great tweak on the format, adding something almost like a puzzle mini-game to the otherwise straight-forward levels. Catalysts are orbs dropped from enemies that will give you buffs, and if you match them properly in a grid you'll get an extra bonus. In co-op you can mix & match them with your friends to go for the best combination, just one more thing make team play really fun. The huge variety of beautifully rendered Heroes, enemies, abilities and environments also help keep the game fresh and exciting, since no two enemies behave the same. 

In the end, this game is as exciting as you make it. If you choose to only play one Hero, switching as little as possible, and never use any abilities, then yes, that can get dull. You also won't make it very far! But if you make full use of your abilities and constantly switch in new and different Heroes, the potential for exciting gameplay is endless. However, PvP needs a lot of work, the game lacks a really in-depth trading system, and the plot is very basic and sometimes even confusing. If those things really bother you, watch some videos before purchasing. If you're looking for an excellent replacement for Diablo II or Torchlight with deeply satisfying, visceral, and surprisingly deep gameplay, though, this is your game!