Well, the 30 free days that came with the game are up, and I'm not renewing.
Champions Online billed itself as a superhero action MMO. I can accept the growing pains typical of any MMO, but the game has much more fundamental problems. The 'action' element is all but irrelevant. You can't miss with a range power, or be missed by one - even if you get out of it's range after it's shot but before it hits you. So, aiming and dodging, two fundamentals of an action game, don't exist here. Blocking theoretically could've added a decent action element, but it's so horrifically unresponsive as to be useless if you intend to use it in an action game kind of way. Mechanically, CO is just an mmorpg - action not included.
And the superhero portion of it....well, the game is balanced like every other MMORPG out there. IE, to ensure the players advance very slowly and thus keep paying that monthly subscription. This may be OK in WoW or whatever, where you're expecting to be Joe the fighter. Unfortunately, CO was selling me on being a superhero, but the best hero you can make is still roughly equivalent to one of the D-List 'superheros' that Marvel creates simply to make Wolverine look more awesome.
So you're left with a typical MMO in silly costumes, still going through it's 'nerf-a-week' growing pains. It's not impressive at all, and it's just not worth $15 a month to cling to the hope they'll finally decide what they're going to do to make the game worth playing.