If I can give one piece of advice about this game, it would be to not formulate opinions of it based on the Walmart demo. It sounds pretty silly, but if you happen to see the game on the crappy display DS and attempt to play it, you will be met with frustration and a bad taste in your mouth. The controls were clunky and unresponsive, and the entire game just felt awkward as I was playing it. And so I dismissed the game, and refused to buy into all the hype surrounding it.
But then I played the actual game. And boy, what a difference that makes. Something about the finished product is much improved from the Walmort demo. Perhaps it is just my refusal to accept the game that made it seem bad. Perhaps it was the huge metal casing surrounding the DS and the thick screen protector scratched to oblivion. But whatever the case may be, just know that Elite Beat Agents is an incredibly fun title on the Nintendo DS, and I encourage you to pick it up.