Muramasa sold about 180.000. I think these are good sales for this type of game.
My list of overlooked games:
1. Boom Blox Smash Party
2. Pikmin 1+2 & Donkey Kong Jungle Beat (much better with Wii controls!)
3. Cursed Mountain (I love the intense atmosphere in this game)
4. Little Kings Story (also I don't find this great THAT great, it is a nice game)
5. Sword & Soldiers (one of the best WiiWare games)