Here is my list of top 10 Silverlight (somewhat competitor to Adobe Flash) games, rated by quality, gameplay, sound / music, design etc. There are lots of crappy Silverlight games out there. Actually, most of Silverlight games sucks hard compared to Flash games.
DaoDao. Connect two tiles. Play Now!
Shinguru the Ninja. Addictive game played only with space button on keyboard. Play Now!
Dr. Popper (ball game). Find and destroy balls of the same color. Play Now!
Silver Arcanoid. Arkanoid / Breakout like game. Play Now!
Dot Killer. Another addictive and hard shooting game. Play Now!
Block Rogue. Interesting and nicely done puzzle game. Play Now!
Area Tower Defense. Classic tower defense game in Silverlight. Play Now!
Mahjonged. Online version of Mahjong. Play Now!
Klotski is a sliding block puzzle game. Play Now!
Ice Breakers. Try to break all ice crystals with falling balls. Play Now!