This is a very difficult game to enjoy, and it's not because of any one thing.
The superhero genre is at its peak across mediums. So, one would expect that with DCUO being one of only two MMOs set in the superhero genre, it wouldn't be difficult all that difficult to make an amazing game. Indeed, this game has some of the best ideas I have ever experienced in an MMO... yet manages to bork the implementation of every single one of them.
First, lets talk about character creation. At first glance, it looks pretty decent. There are a fair selection of quality starter items, and lots more can be unlocked by playing the game. Unfortunately, those unlockable costume pieces are unlocked *per character*, which means you can never actually start with the character look you *want* to have. In some cases, unlocking the pieces you need to complete your character's look can take *weeks* of grinding for *hours every day*.
This purposeless, artificially-limited aspect of the game has all but destroyed DCUO's role-playing community. And if you know anything about the tight bonds that role-players bring to a game, then you'll recognize the assinine idiocy behind the way this game's character creation continues to be handled.
On a somewhat less-intolerable note, the colour pallet is limited to storing four colours. They can be any colours you want, but once you pick them, all of your costume pieces are limited to those four colors.
The power and weapon sets in this game are probably it's biggest boon during power creation. They really are fantastic, even if some of them are locked away behind paywalls.
The missions are fun and not too tedious, even when replayed. And there's lots of raids, PvP, and open-world events, too.
DCUO is often compared to Champions Online, the only other active MMO in the genre. This game has better gameplay, a better setting, better combat, better enemies, better raids, and better overall content. Yet, DCUO universally considered a vastly inferior product based almost solely on gamers' (in)ability to create the character appearance they want from the start.
Ultimately, if you're looking for a game to create the superhero of your dreams, go for Champions Online. If you're looking for a game with an active community, go for Champions Online. If you're looking for a game to role-play a superhero of your own creation, go for Champions Online (or Paragon Chat). If you're looking for a game to play with friends, go for Champions Online. But... if you're looking for a game that has great content to solo, and you don't care about how your character looks, or that lots of powers and weapons are stuck behind payways, and you only intend to play one or two characters, then... THEN... consider DCUO. But honestly, you'll probably have more fun in Champions Online--which is sad, because Champions Online really isn't that good of an MMO.