Another World
A free version of Another World has just been released for the GBA. (Beware; the person who runs that site seems to be something of a furry. Safe for work, but kind of sad.)
For those of you too young or too forgetful to remember it, it was a lovely early polygon-based adventure game, where you control a scientist who’s been transported to a strange world after an accident during a particle accelerator experiment.
Eric Chahi, the original creator, collaborated with Cyril Corgordan to make this GBA version. Since it’s just a ROM image, not an actual cart, you’ll need either a GBA flash cart, or an emulator to play it.
It’s a really short game, but expect to die a lot. It’s not always clear what you’re meant to do, but its set pieces were totally unmatched until Half-Life came along. (Well, with the possible exception of Flashback, its sequel-of-sorts.)