Played it for about 3 or 4 hours today w/ my gf's daughter -- picked it up with a bunch of the packs for the PS3. I gotta say, it's pretty fun - besides the combat, there are a lot of little puzzles to do. With each character leveling up separately, having hidden skills you have to find, and being able to purchase new abilities - there is a lot to do if you're one of the type that likes to complete stuff.
While the game is pretty simple, the abilities make it fun - especially in the 2-player competitive arenas. The kid I was playing with got a kick out of the interactivity of the arena's - she loved flooding them with magma or triggering spike traps.
The versus modes are fun, I just don't know how long they'll last -- that part of the game really needs to be able to play more than two. If you could play four, it would be pretty amazing. There are 3 different modes, all relatively different. One is a simple battle level, the other is like football -- you have to get this energy orb and make it into the goal zone for 7 or throw it through the uprights for 3 while the other player tries to take it away. The third is totally an homage to Power Stone -- you have to collect 5 power stones that spawn on the field. Hitting the other player makes them drop the stones.
There seems to be a good variety of enemies and the different powers of the creatures makes for some good combos -- they all feel really different due to their offensive/defensive powers.
The switching out of characters on the fly is seamless and easy - it works really, really well - to the point that if one of your guys is about to go down, you just grab it off the portal and replace it with someone new. If you put back the old figure, it remembers the damage level. Pretty cool.