Bit.Trip.Runner is an interesting platformer, and very different from Beat, but be warned that it's somewhat tough, and fairly leveraged on memorization.
Lost Winds: Winter of the Melodias is a big improvement over the original game, and I enjoyed this one (the original? Not so much). But it retains the more mellow mood of its predecessor: don't come looking for a challenge, since you're just going to get four hours or so of calm exploration.
Swords & Soldiers is a great 2D RTS: the campaign mode will take you several hours, the challenges add on some variety, and the multiplayer can be quite fun. Be warned though that it is very much a streamlined RTS: there are a very limited number of units you can choose from, and once you build them they act almost completely autonomously. You still have a lot of control over the field, but don't expect it to be like any other RTS you've ever played.
Cave Story is f***ing awesome, and probably the best choice of the games you listed. Screw that, it's probably the best game on WiiWare. Or any of the digital services. Think Metroid, but longer and with more choices to make.
NyxQuest is about three to four hours, if you want to unlock the last level. It's a good 2D platformer: the environment is a much bigger threat than the enemies, and it's mostly leveraged on your ability to rub your belly and pat your head at the same time.
Rage of the Gladiator: I haven't played this one, but I've heard that it's a decent Punch-Out!! clone with much lower visuals and much less craft involved. The biggest problem I've heard is that the fights drag too long, but if you liked Punch-Out!! a lot and are wanting more, this might be the one to get.
Art of Balance is highly underrated: it's a great hidden gem, and although my hands-on time with it was pretty limited I enjoyed it, and I've yet to hear anything bad about it.
Excitebike I haven't played.
Blaster Master:Overdrive is a good sequel to one of the best NES games, but it definitely can't hold a torch to its predecessors. Most of the boss battles are great fun, especially towards the end, but the tank is less fun to play with than the original, and the developers made way too many elementary mistakes that are, simply, mind-boggling. That said, I liked it well enough, and you probably will too if you're a huge fan of the original. Save points are a nice addition: their placement is not (see: elementary mistakes, supra).
Art style, beats me.
