Fire 'N Ice is the best puzzle game, on any system, period.
There are 100 levels separated into 10 worlds. If you beat the game and wait after the credits for some time, the game will tell you how to unlock 50 more excellent bonus levels (hold select at the start screen and press b 10 times). Things start out easy at the beginning, but quickly start to test your mental skills. Most levels can be done within 5 min but many will keep you stumped for 20 min or more.
The graphics for the game are some of the best seen on the NES. It has a whimsical storybook feel to it, especially considering the story in the game is supposedly being played out while being read to children as a bedtime story.
Playing this game for hours-on-end late at night with The Smashing Pumpkins' Melancholy double-album playing on loop is one of the most relaxing experiences you can have. Sometimes you just need to escape, and this game provides just that. Even though there are plenty of levels, plus a level-editor, I still wish it was longer. And Solomon's Key, the prequel to this game, just isn't as good.
Ah well. I guess I'll play some Adventure of Lolo...