I picked up D.O.N. on Gamecube the other day and its pretty decent IMO.
All of the characters I've tried so far feel quite different from each other, no real clone characters like Smash Bros. The gameplay is fairly simple: B is your main attack, A is jump, Y is a character-specific attack, Z is for throws, L/R are block, and X is for supers. Each attack can be changed by pressing a direction similar to SSBM (example: Up + B is a different move than Forward + B). The stages are a good mix from all 3 animes, and the graphics/animation are pretty damned great.
My major gripe with the game is the way you have to unlock stuff. During the game you are given a mission to complete during each fight. Pass the mission, win coins. If not, just continue on to the next fight. After you beat the game, you use the coins in a big slot machine (1 pull = 3 coins) and you have to line up 3 of the JUMP icons to access a SECOND slot machine where you have a chance to unlock stages, characters, and gallery art. It is the biggest pain in the ass EVER.
For example, I beat the game on Very Hard mode and had 150 coins in the end. I was only able to get to the second slot machine 4 times, and out of those 4 times I unlocked 1 stage. Absolutely ridiculous.
I haven't touched multiplayer yet, but it seems like it could be fun.