I like the fact that the team took the design philosophy from City of Heroes that worked (quick to play, easy to pick up, lots of customization for the player, and minimal grinding with the exception of special player rewards for those who do them) and expanded it further. It was the idea that playing the game is the reward rather than reaching the top level or finding the special items and it makes the game very friendly to people who don't necessarily have a lot of time. It's a concept that makes the game poison to those who obsess over their MMO's but there is a market of people out there who want that kind of thing that is barely being serviced.
I'm enjoying the huge creative zone design. It feels like a comic from the 1980's to me; still holding onto the cheesy lunacy dreamed up in the 1960's for kids but trying to dress it up in something for a slightly older audience. So you've got Monster Island with giant monsters, Dr. Moreau, and a fallen ancient empire in a volcano. Or in the desert a Hulk-knock off leaps around and fights whatever (player or enemy) happens to be underneath him when he lands whether it's the secret base where there's a UFO, Westworld style amusement park, or the ghost town. The maps and enemies are wonderfully, cheerfully, crazy as you'd want in a superhero game.
The problem is that there's just too few. There are a couple of gaps in content with the game at the moment and only five zones. Champions needs at least twice as much content as it currently has mainly because it's so much fun playing with different kinds of characters; when every character has to do nearly everything then it isn't as fun to change from your flying fire guy to your robotic battle suit guy.
On the other hand there's giant piles of supervillains to fight. If there was one thing City of Heroes lacked it was villains. Now there's a supervillain around every corner and quite a few just wandering the map. In one mission I even came across an entire team of Soviet supervillains that I wasn't expecting. There's a lot of them even without making your own and many of them come back.
I like the variety of powers and how you can mix and match pretty much anything. On the other hand I'm not happy with how the buff and debuff abilities are generally weaker. There aren't a lot of them at the moment (at least ones not tied to attacks) and the game really needs a bit more of those for flexibility in character design.
Speaking of character design, the fact that the customization has gone even further is great. They took a terrific system and made it better by allowing asymmetrical options.
So in short, I'm having fun playing but there's too little there for the time being. Maybe six months from now once the new MMO problems have died down it'll be really spectacular.