I now own New Super Mario Brothers, and it's fun but way too easy, I completely finished the game within two or three days. I also have the newest Yoshi's Island game which is just as good as the original, in my opinion. The Sonic games on DS aren't bad either, but the voice acting is beyond annoying.
To whoever posted Flashback - what a game! I bought it second-hand though and someone had written all the passwords on the instruction booklet and curiosity got the better of me, bah. Still completed it myself though, eventually.