Cryptic didn't deliver a valid successor to their previous game.
Yes, ok, CO's character creator is another leap forward from what offered the beautiful City Of X creator. And the free-form power choice is a nice introduction (but it has the drawback that FOTM powers are a must and are usually taken by all characters).
But apart from those two brilliant pearls, CO doesn't give an interesting experience. The game is easy, very easy. Too much solo oriented (something that's deeply different from a game that's solo *friendly*). Too few content (replayability is very low as you have to do mostly all the content to reach max level). No endgame intriguing content (just some repeatable missions). A lacking PVP (few type of games, no arranged arenas between teams, with rewards mostly useless or not worth the effort).
In the end a game with an immense potential ruined by poor design choices (such as the missing scalable missions) and a terrible absence of enough content to keep it interesting.
You may play it for the first month and love it, but then you'll ask yourself "is that all"?