Ok so DC Universe Online just came out a few weeks ago, and I've been playing it non-stop. I have been playing it as such not because its unputdownable (rah new word), but rather because I've been trying to figure out how to describe it.
It is at its base a button mashing, puncher, platformer taken to the nth. You have two attack buttons, one jump button, and an interact button. So it kinda plays like one of those side scrolling beat-em-up games like battle toads or something. Fairly straight forward. They expand it by giving you button combinations to execute combos, and specials (mainly by holding down R2 or L2 and then hitting one of the four main buttons), but really most things can be accomplished with the main combination. They take a stance based variation on how you select your role for the group. In one stance your damage, another your tank, and another your a healer. All stances do damage, but for instance in a healer stance your damage spells also heal those around you. When you make your character you not only choose hero or villian, and sex, but you also choose mentor and power type. No one power type gets to be all 3 roles in a group, and when you spend your power points you be come better at one role than another. Choosing mentors dictates where you start, and who you have most contact with as you level, for instance you choose superman he contacts you more than others, and you get benefits from choosing power types that go with him best, for instance ice or fire.
The world itself is large but not as big as say world of warcraft but it is detailed and the poly count is much higher than WoW. Metropolis is the largest city by far and both wonder woman's desciples and supermans start at. While Gotham City is slightly smaller and darker but still very large overall and where Batmans desciples start. The Watchtower is also completely modeled and the fact you can fly, run, and climb all over everything means that they spent time making everything look good and well detailed. That being said most things need a little more time on the texturizer. It doesn't really make use of all the power the PS3 has to offer, but it looks better than WoW on many levels.
This being said, its still glitchy as all get out. They seem to have fixed the problem with it locking the system up, but there are some animation glitches, and sound glitches. For instance the sound effects fade out some here and there. Some of the other down sides are lack of function with some of the PS3's capabilities. Some Wifi capabilities are iffy, and there are voice issues. Not to mention the fact that chat is nearly impossible without adding a keyboard in someway.
What makes up for all this is the travel modes. You get to select from flight, super speed, and acrobatics when you make a character. Flight is pretty simple, double jump to fly, press forward to fly forward yada yada. Acrobatics is pretty much a mittle ground you run fast on the ground and can climb up anything, as well as being able to leap and glide. But the fun one is super speed cause its just so cool being able to just run where ever you want. You can take off running in just about any direction, even over water, and up the sides of buildings. There are times when you make a leap of faith to go from platform to platform. Coming from WoW with fall damage to this with no fall damage, makes you take a breath each time you leap of faith. Its actually quite fun.
Either way inspite of its issues its lots of fun and pretty easy to play.