Gloop is my favourite out of the ones listed. There was also a commercial version called "GloopDX".
My personal favourite homebrew GP32 game is
Bolcataxian, which is quite simply the best 2D shooter I've played on any console, period. It won first place in ADIC2004, but unfortunately, JBB stopped working on it because the sponsors of the competition reneged and didn't send him anything. That was a real loss, as it was a really fantastic game with very well-balanced gameplay mechanics, and I would have gladly paid money for it if it were completed.