Pokémon Pinball:
If you like Pokémon, pinball or both, this is really one of a kind (well, there's also an inferior GBA version). Basically, you play pinball while you try to capture Pokémon using the pinball mechanics. You can evolve them and complete the Pokedex (which btw has some very interesting entries different from the ones in R/B/Y.). Also, you can travel to different areas which have their own Pokémon and face very challaneging and fun bonus stages that give you tons of points. You can even save the game at any time, so you don't have to worry if you were having a great run but you have to go. It also has a rumble feature via AAA battery, something not many GB games had. The only negative thing I can think of is that, like in real pinball, sometimes the ball will go directly to the bottom and there is little you can do about it. Although in this game some of the GB buttons make the screen tremble in a certain direction, which can save you sometimes.
This is one of my favourite GBC games, no doubt. I'll think about a few more I have in mind...
