Advance Wars 1+2
Banjo-Kazooie Grunty's Revenge
Beyblade V-Force
Boktai 1-3
Breath of Fire 1/2
Bubble Bobble - Old & New
Castlevanias (all)
Classic NES Castlevania
Contra Advance
Crash The Huge Adventure
Crash 2 N-Tranced
DK King of Swing
DKC 1/2/3
Dr. Mario & Puzzle League
Drilldozer
Final Fantasy IV/V/VI Advance
Final Fantasy Tactics Advance
Fire Emblem
F-Zero
Golden Sun 1+2
Gunstar Super Heroes
Kirby Nightmare in Dreamland
Kirby & The Amazing Mirror
Konami Collector's Series - Arcade Advanced
Kurukuru Kururin
Link to the Past + Four Swords
Minish Cap
M&L Superstar Saga
Magical Quests
Mario vs Donkey Kong
Mega Man Battle Networks
Mega Man Zeroes
Metroid Fusion
Metroid Zero Mission
Mother 3
Namco Museum
Pac-Man Collection
Pokemon Ruby/Sapphire/Emerald/Fire Red/Leaf Green
Pokemon Mystery Dungeon - Red Rescue Team
Sonic Advance 2+3
Street Fighter Alpha 3
Super Ghouls'n Ghosts
Super Mario Advance 1/2/3/4
Super Monkey Ball Jr.
Super Puzzle Fighter II Turbo
Super Street Fighter II Turbo - Revival
Teenage Mutant Ninja Turtles
Wario Land 4
Warioware Mega Microgame$
Crash Bandicoot: The Huge Adventure
Crash Bandicoot 2: N-Tranced
Crash Nitro Kart
Crash Purple: Ripto's Rampage
I really loved the Crash games for GBA. Pokémon too, but those are already up there.
I liked the platformers, and I did play a lot of crash nitro kart though I don't know if I would call it essential. Crash Purple, though, I would not recommend at all, and I say that having 100% completed it. It's better than Spyro Orange but dear god whoever thought it was a good idea to make it a minigame game needs to get thumped over the head.