I was in beta for DCUO on the PC, I don't have a PS3. I really enjoyed the combat style and the game overall. A few things that ultimately made me decide not to get it though.
Controls. I'm not found of the control system where moving the mouse also moves the camera around at the same time and you are forced to use WASD keys. I don't typically use WASD keys to move around since Ive never had to use those in games I play.
The Interface. The interface not being customizable was a let down. Not even being able to move elements around. Having to hit escape to gain any mouse control. During beta at one point, I got a buff on my character and I wanted to know what it was. However, you can't mouse up to find out, hit escape and the character frame disappeared. Really bad with the interface.
Mission Tracker. Not being able to remove missions from the log. This was brought up during beta and a developer stated they had no intention of allowing players to remove missions.
Chat System. This is such a horrid chat system. It got better by the end of beta, but it was still really limited. With the way the chat system is with little options or control over it, it felt more like a solo game with a chat box.
All of these things were brought up on the beta forums, but Sony didn't listen to the feedback, at least not yet. They are too big, have too many other games to really care. It's too bad really because I think outside of the MMO elements, the game is fun and would be more enjoyable even as a single player game. It's just not worth the sub cost to me.