I bought this on PSN recently ($9.99, IIRC).
I haven't played it since my post-demise Dreamcast was put away.
It looks fantastic on the Vita and plays great. Tragically, there is no WiFi fighting (and if this ever comes to XBLA/PSN, they'd better update it appropriately), but just playing it again, your first thought is always, "Why the hell is this series dead?"
It is so good, fun, and unique (still!). It's easy to grasp, conceptually, and as pick-up-and-play as they get.
My only gripes are the way the single-player portions play out. The first game makes you play through all the stages in one go. The second game has you choose stages, but they're all open at the start, and there doesn't seem to be any unlocking going on. Also, again, no WiFi mode, and this game is clearly meant to be played with other people.
But other than that, it is just fantastic. The gem collecting adds a perfect element to the game that I'm shocked no one else has picked up yet. For those that don't know, you start with a gem and so does your opponent, when you pound on them enough, their gem comes free and you can collect it. Sometime later a third gem appears in the stage, get that one, too and you go into a super powered-up mode (different for each character) that will likely kick your opponents ass. Of course, your opponent is trying to do the same.
In the meantime, chests are being dropped that offer health and weapons, plus, there are traps to trigger in the environment (the second game does this really well). And it moves fast. These games both somehow manage the impossibly perfect and elusive controlled chaos. There's insanity going on on the screen, but you do feel in control of your area of it and can have a corner of your eye on the rest of it. The only other game that handles this as well is Bomberman.
So why the hell do we not have Powerstone 3?!