There is no secret that I have been playing Champions Online for about a month now. It's a great game, and the only downside I can see it having is that there might not be an endgame, but with 8 total characters by default (you can buy more), top notch graphics, sound, stories and immersion the game is tops in my book.
The real beauty of the game is that it does SuperHeroes well. Cryptic is the studio that also did City of Heroes/Villians, so this wasn't anything new to them. I didn't play CoH, but you can tell they definitely had things thought out. It's nice to be able to create a character with powers that feel like their own, even if they are the same thing someone else can pick up. I can say that so far with the exception of the various Hulk/Mr-Fixit's running around (I've seen about 4 total) most people are creating their own hero.
The immersion is superb. You will feel like you're fighting comic book gangs, mystics, ninja, terrorists, demons etc the with every fight, and although the combat can get a bit repetive when you only have a few powers, the fights themselves aren't always a walk in the park. And for fun they even throw in timed scenarios that reset and run again every X minutes, or random Legendary villains that can only be beaten with a team. Expect to die a couple of times to the cosmic villians. That's just their job.
Now all of that isn't saying anything about the art. The art style is so appropriate to the game. and the options are so varied that creating the same character from an idea will still get you multiple different looks (e.g. the multiple mr.Fixit's), and don't worry about having the same name. Your toon is associated with your login name, so if you a toon named spider-man, it won't already be taken.
Now the only real downside I can see to the game isn't so much balance as it is balance concept. They are still tweaking powers set to make sure nothing is overpowered. This is a good things, but some of the tweaks might end up changing the way you play. The good side though is that for every major change they make to a powerset (which actually hasn't happened during my month time), they offer a free Retcon, where you can go back and change out your powers, or the stats you purchased.
The benefit of it being free is the major nice part, but you can always retcon your toon with in game cash at any time. The main downside, the further back you want to go, the more expensive the change, and changes have to be done in layers, that is to say you have to undo the last, then the one before it, etc. It would be nice to be able to just go to the power you want changed.
The counter to that though is that you really do end up trying to decide what's in the best interest of your toon. It's a tough call to take which power you think will help.
And honestly that's something I expected from a MMORPG based on an actual RPG.