City Of Villains is actually the best MMORPG out right now, IMO.
It's the only MMORPG to use a physics engine which it puts to spectacular use with minions flailing around like rag dolls and bouncing off railings and collapsing to the ground....like you'd expect from a superheroes attack.
Groups are totally free-flowing. There's no need for a nuker or tank or healer until you get to very high levels and, even then, one defender or corrupter is usually enough to buff/debuff your team to victory.
The number of side quests is actually surprisingly high and you'd never know 75% of them were there unless you ended up in a group with a leader who already knew about it. The Shivan quest for example which gives you an Elite Boss pet reuseable 5 times.
Character customization. First of all, the character generator which is still second to none. Incredible flexibility and chance to look truly unique. Aside from that and more importantly, there are so many classes and power sets within classes that you can configure a character to your exact personal play style. There's not just a tank. To clarify, you choose a primary and secondary power sets of which there are at least a half dozen to choose and each powerset in your primary and secondary and the combination thereof, is what defines you, so within each class you have at least 36 combination which are each distinctly different from each other and which ever one you are will have a direct effect on how the groups you're in will approach missions.
That said, it's still extremely shallow beyond PvE combat and combat itself gets repetitive really quick. So this is still a very limited experience, but it's not cut from the EQ/WoW/DAOC mold so it deserves that much credit.