Harry Potter and the Chamber of Secrets for GBC.
Don't laugh, go play it!
It's among 2 turnbased games I like. The other being the flash gameseries Sonny.
Flaws include:
-Sticking to movie plot, thus killing a lot of options.
-Giving you 1 character to dress, but taking her out halfway through
-Having you upgrade spells all the game, but taking away your wand in the final battle
-Being very short
-All equipment is in the same ranges: defence yahoo. I'd liked to have a choice between +agiliy, +attack and +defence in stead of the easily obtainable coat with the absolute highest stats of everything else you'll get.
Things that make me like it:
-A fun little fetchquest, but it can be solved before your first class, so that's rather stupid.
-A card colleciton minigame with in-game bonuses for getting all cards of a series.
-Having likable minigames like bowling, but also quiditch.
-Having a huge bestiary for you to fill, I need only 3.
-Having a great map. It's big, but not huge. You get to know it pretty fast, but still have to use the map every once in a while.
All those flaws are annyoing, but I finished it over 20 times. It's just THAT good!
EDIT: Lol, I got ninja'd by the guy above me!