Sonic Battle is an above average game. But if you expect a portable Super Smash Bros., you will be terribly disappointed. The single player game is very short and repetitive (and also a tad too easy). You basically play the same fights over and over again in different locations. The multiplayer isn't much better. It reminds me of a button-mashing fighting game, don't get me wrong those can be fun, but they get kind of old very fast.
I don't want my negative tone make you pass this game up. It has lots of strong points too. The graphics are the best on the Gameboy Advance. The game's mechanics, though a little disappointing, still provide some fun. This would be a title to pick up used, or at least discounted.