Lufia: The Legend Returns (Neverland/Taito, 2001)
It has good music and a unique battle system that seems to use a 3x3 grid of party members, but despite being a release from 2001, its story and interface feel straight from NES-era JRPGs. It's full of stilted dialogue and needlessly complicated menus. Critics at the time seemed to agree, as it received pretty poor scores across the board.
M&M's Mini Madness (Pipe Dream Interactive/Majesco, 2000)
I had the PC version of this as a kid and loved it, so I was very sad to discover that the GBC port won't get past this startup screen in any of the versions I have access to. Alas. Maybe I'll be able to track down a used cartridge eventually.
Macross 7: Ginga no Heart o Furuwasero!! (Aisystem Tokyo/Epoch, 2000)
It starts out with a really long static cutscene about all the characters playing in a band, and then suddenly the go to space and it's a shmup. Not a very interesting one, either. It feels like this is probably based on some manga I've never heard of and was trying to trade on that brand rather than anything of its own.
Madden NFL 2000 (Tiertex/THQ, 1999)
I don't pretend to be any kind of an expert in football games, but this pixelated mess has got to be one of the worst. It didn't even bother with player names, and you'd never guess that the teams allegedly represented above are the Colts and the Broncos. That said, this is notable for being, at least on GBC, the only one of the Madden games to release in the EU, for releasing there earlier than in the US, and for not having any involvement from EA Sports in the US.
Madden NFL 2001 (3d6 Games/EA Sports, 2000)
This one did not come out in Europe and did involve EA Sports. It maybe looks a little better, but it still doesn't pretend to represent any players and those teams don't look a whole lot more representative of the Titans and Rams than the teams above did of their counterparts. It's pretty much identical in terms of gameplay, but they did upgrade the menus a bit.
Madden NFL 2002 (3d6 Games/EA Sports, 2001)
In what would become a tradition for EA Sports, this is literally just the 2001 game again. The menus have not changed, the mechanics have not changed, and since it never had player names in the first place, the teams haven't even particularly changed. You're supposedly looking at the Ravens and Giants above.
Magi Nation (Interactive Imagination, 2001)
A spinoff of a collectible card game I've never heard of that seems more obviously inspired by Pokemon. You play some kid who gets sucked into a magical world where people tame monsters by beating them up and then use them to beat up more monsters. I didn't get to see combat, and the music is of deeply inconsistent quality. Still, it has a great sense of humor, beautiful graphics for the time, and an interesting premise, so I'll be coming back.
Magical Chase GB (Micro Cabin, 2000)
A shmup that's not particularly interesting other than having some crazy enemy designs.
Magical Drop (Conspiracy Entertainment/Classified Games, 2000)
A puzzle game where you can grab colored orbs and then shoot them back at matching colors to make them all disappear and get points. It's mostly interesting because the little jester guy can hold a huge number of orbs at once, so you can shoot back a massive column and clear a whole color quite easily. I'm not actually sure where the challenge comes from or why you need to pick a character to walk through the void in the background, though.
Magical Tetris Challenge (Capcom, 1999)
Seems to be bog-standard Tetris with Disney characters doing interpretive dances off to the side. I'm sure that concept appeals to someone.
Golf Ou: The King of Golf
John Romero's Daikatana
Kakurenbou Battle Monster Tactics
Keitai Denju Telefang
The Legend of Zelda: Link's Awakening DX
The Legend of Zelda: Oracle of Ages
The Legend of Zelda: Oracle of Seasons
LEGO Island 2: The Brickster's Revenge