Super Mario Kart battle mode may be the best one, even if it's only 2 players. Everything from the weapon set to the battle arenas is so simple, but that's what makes it so good. It's why I like playing Mario Kart 7 battle with bob-ombs only -- it replicates the simple nature of Super Mario Kart's battle mode.
I already own Cubello and I have no interest in Radar Mission. Is Mario's Picross worth it even if I already own Picross DS? Weren't a lot of the downloadable puzzles from Mario's Picross, meaning I've played most of these puzzles?
Hm, I think I'll jump on Mario's Picross for sure. And I've got some coins to burn, so... Radar Mission... tempting. I know nothing about the game, and I've not played it before. I guess getting it "for free" would be pretty sweet way to check it out without much risk.
Cubello is one of the better Art Style games. It's pretty simple in that you shoot coloured cubes at a structure in order to match four cubes together, and they disappear. The goal is to eliminate all the blocks from a structure. It can get hectic, and it takes some planning ahead to finally clear a stage properly. It has a cool endless mode to boot. For 100 coins, absolutely recommended.
Mario's Picross - definitely giving this a download! I had a hunch it would end up on Club Nintendo. This should hold me over until we get Picross-e.
Radar Mission - never heard of it. Will most likely avoid.