GBA is very well documented (gbatek). The DS seems to be as well, but it's much harder to work with. GBA is much easier, but still powerful enough to do non trivial things without having to do them all in assembly. Emulator support is superb. Hardware adapters that allow you to load ROMs have been around forever.
I'd say it's one of the best systems to get into on-the-metal Homebrew.
There’s more potential complexity if you want to do complex things and maybe 3D is hard (I’ve never done it) but the basics are about as straightforward.
Fair enough. Id say 3d and the two screens make it harder. Also memory latency and clock speed is somewhat more complex, what with the tightly coupled memory.
Low resolution combine with a decently fast processor means software rendering is entirely doable. It's a comparable situation to very early PC 3D gaming.
It's especially crazy that a bunch of them look to be rendering legit polygon scenes— this isn't early nineties 2.5D titles like Doom and Wolf3d running on 486 PCs.
Ok you could argue that’s more complex on the GBA.
I would argue otherwise; interfaces to other people’s stuff always are the most difficult parts of programming. When you do it yourself (3D projection etc.) it’s just you and reason and that’s not so bad.
4 MB RAM + 656 kB VRAM doesn't strike me as particularly memory constrained as someone who grew up with 4-64 kB systems. I guess it matters where you're coming from.
I'd say it's one of the best systems to get into on-the-metal Homebrew.