The Gameboy Advance was a great disappoint for me when I had one but now I miss having one. but I if was to pick 2 it would be.
1: The Sims 2 Pets for GBA. this installment in the famous people life simulator. Was like an RPG with The Sims gameplay but leaning more toward being an RPG. You had a character, you had to take care of like Bladder Food and Hygiene I think. But That is all I remember. But it was nothing like any Sims game on the PC.
2: Duke Nukem Advance a first person shooter with clunky controls and lots of lag but still playable, But it had early N64/PS1 style graphics and althouh the graphics were the exact same as Duke Nukem 64 or Duke Nukem 3D, so maybe that Duke Nukem game was too powerful to run properly
I might pick one up again, if I can find an SP for under $200 USD