[k0k0]

My absolute favorite downloadable game is Shadow Complex. It's single player but for the price, you get a whole lot of exploring, shooting, and cool stuff going on. It's kind of set up like metroid in a way but it's awesome.

I love Guardian Heroes too. But you'd probably want to try it first since it's a Sega Saturn port and they messed with the art style a lot for it. It is multiplayer though.

I also love me some Trials HD, which is a really hard platformer type game using a motorcycle.

I loved the splosion man and ms. splosion man games. Although multiplayer on those is just too hard. And it's also a platformer.

Really, for any downloadable game I'd suggest trying the demo first to see if you like how the game plays.