Literally the best MMO on the market today.

When I'm in the mood for a loot grinding, kill the baddies, take thier stuff, ARPG, I could play Diablo III, which has become boring for me, or I could play Marvel Heroes. 9 times out of 10, I'll play MH. The action is solid, the loot grind is real, more characters are added on a regular basis to keep things fresh, and best of all, it's free to play. You never have to spend a dime in this game to get anything which affects gameplay, although, if you want to, the option is there.