I Recently bought this game, and was EXTREMELY satisfied, the oneplayer mode is tough, with lots of differant modes to play through
this game is actually Power Stone 1 + Powerstone 2 from the dreamcast basically stuck onto a UMD for us, and you can play both games, i've been mainly playing Power Stone 2, as i am familiar with it, and it has been great fun, and when i took a quick go on Power Stone 1, though the lack of a 3rd and 4th player options for bots or players, it is still a brilliant 2 player and single player game
my advice, get this game, even if your friends dont want it, you can game share, (basically use 1 UMD + 4 PSPs to play your game) bringing the multiplayer theme of Power Stone back.