1. It's really hard to choose what I like the most lol. Gear and world aesthetics, all-in-one class system, DoH and DoL, the main scenario quests and how you never run out of things to do (different logs are a nice touch).

2. I haven't played many other games because I tend to commit my gaming time to an MMO, but I really liked Portal and Portal II. The second one had some kind of team play option to solve spacial problems but they are mostly single player mode. If you like raiding with a static, you could try WoW again. It still makes top quality raids and has a solid theorycrafting community if you like pushing your class to it's limits. The rest of the game is kind of bland though. Maybe the new expansion will spice it up.