Breath of Fire 2 Let's face it, it's not easy for a developer to make a game on a gameboy be emotional. They succeeded with BOF2 and its unique characters, intruiging narrative and such keeps you gripped.
Broken Sword: The Shadow of the Templars Sure, it looked a lot uglier than the PC counterpart but ultimately the handheld offered the full experience of the best BS game with its only flaws being a slightly problematic control scheme and the lack of voice acting (which was incredible).
The Lord of the Rings trilogyOkay I'm cheating a bit by putting 3 games in one, but honestly, Lord of the Rings offered me so many hours of undeniable fun. The first game played out like an rpg with turn based battles and such, the next two were more fast-pace hack n' slash games. All of which were incredibly enjoyable, had a nice soundtrack and even nice visuals for a handheld game, like whether you're in rivendell, moria, minas tirith or lothlorien.
Harry Potter and the Chamber of SecretsThis was the age of good game tie-ins for films. The Chamber of Secrets had 5 completely different versions made, all of which were of a good standard at least! My third favourite of these games was the gameboy advance version (over the ps1 and gbc versions). It's just exciting exploring hogwarts on a tiny games system. The graphics were actually quite nice and the music got bloody addictive. There are also so many secrets to uncover!
Mariokart Super CircuitTo this day it's impressive how they brought the Mariokart series onto nintendos weak little handheld. It performed so well and the game didn't feel inferior to previous mariokart games. It was a perfect handheld alternative and did not disappoint.
Yoshi's IslandThis game is just inspiring. The world was a place I could let lost in and not want to leave. The game's beautiful, the storylines adorable, the music is flawlessly good. For a side scroller this game was bloody amazing.
Baldurs Gate: Dark AllianceA large rpg with a good amount of exploration in an intricate world? Seems it worked just fine on GBA. Admittedly I've never completed the game, but damn it's good. About as deep as an rpg can get on the system.
PokemonLets be honest... everyone loves pokemon.
WariowareBoth Warioware Twisted and Warioware Inc are extremely addictive games that provide so much entertainment in as short as 10 seconds and as long as you want.
Stuntman AdvanceGotta be honest here, the game is addictive as hell. Car/racing based games don't always work on the gameboy advance but this is sure as hell one game that performs excellently. If you're unfamiliar with the Stuntman formula, it puts you behind the wheel and makes you do chains of stunts for films. This means you'll drive through varied and awesome sets and pull of some ridiculous moves. Advance does a great job of bringing the experience to a handheld.
Winner.....
Not sure. These are all awesome games and there are many others that deserve a mention like Duke Nukem, Sword of Mana and no doubt many others that I've forgotten.
Now.. your turn