I've recently in part thanks to the retron 5 decided I wanted to get back into playing more with the GBA and have snapped up some fun stuff the last couple of weeks from legit releases, to homebrew and imports too. I think the system over all has aged incredibly well and probably in no part thanks to tablet/phone gaming and how a good bit of it is designed still feels like it fits in with the modern era quite nicely. Some of those titles have even been brought over from similar hardware like the Square SNES titles that made it to the GBA and then iOS and Android too.
It's fairly easy to point out franchise stuff from Nintendo and third parties like Konami with Castlevania and Capcom with the fighters and Mega Man spinoffs. Amazingly even in a few cases some fairly solid ports from even the PC made it over which was a surprised like the very faithful DOOM 2 and Wing Commander Prophecy with its 3D engine recreated pretty nicely.
I cant recommend the homebrew Qwak enough, a conversion by the original maker for the GBA as I've been having fun blowing time on it in a free moment. From overseas in both directions I got an english version of Kurukuru Kururin and also a Hudson Selection package with both NES Bomberman titles on it recreated faithfully. Car Battler Joe is a big Natsume game that falls well under the radar that few copies show up online for and it's like the fun mad max meets anime meets delivery service game that's just straight up unique and well designed.