My wife bought me a zip lock bag full of GBA titles at the flea market. Mostly little girl games but some decent titles too like banjo pilot and a port of sonic the hedgehog. That bag has put me over the 1000 game mark.
I hear that the GBA release of the original
Sonic the Hedgehog is one of the worst ports ever. Apparently there's a lot of lag involved. Best to send it over to Razor Knuckles and wash your hands of the whole horror show.
Myself, I re-milestoned a recent un-milestoning by getting back up 200+ full PS1 games.