I think there's been a huge missed opportunity for Nintendo over the years. Instead of making it easy for home brewers to write stuff for their hardware they do everything in their power to lock it down. I never could understand why Nintendo didn't embrace the home brew community. I understand the issues with piracy but if they made the hardware available for custom apps then perhaps there wouldn't be a need for hardware like the R4.
I actually really liked the GBA, since it's what got me started in the home brew scene, and then of course, the Nintendo DS. Writing Warhawk DS in 100% ARM ASM with Flash (with graphics by Lobo and music by SpaceFractal) was some of the most fun I've ever had and my first major collaboration. I think schools should be teaching kids ASM using the Nintendo DS. It is such a great way to learn low level programming and assembly. NDS is the last hardware, I believe, to support the 2D sprite system (based in part on the NES hardware), and in addition introduced basic 3D hardware. With Warhawk DS we used the 2D hardware while smealum's impressive Arsenal DS used the 3D hardware. I think later Nintendo hardware removed the 2D system which is a great shame as it's such a great way to learn game programming.
Incidentally we did get a chance to play with the NDS's 3D hardware when we started playing with Jungool (originally called Triball). Unfortunately though with the limitations of the hardware it didn't fit well with that sort of game (Box2D physics / large painted backgrounds rather than tiles). But not only did we use the NDS for an early prototype of Jungool we also started an early version of Windoze Solitaire on it. Both of these games ended up being ported and released to Apple's iOS.
Over the years it has got to the point where I've given up on Nintendo and do not want to support them anymore. I don't like closed systems. I've also moved away from iOS to Android for the same reason. But as far as writing games both Flash and I have moved on from ASM / C++ to C# and Unity. That being said with hardware like the NEXT there are still opportunities to work on limited hardware. For me personally though I want to concentrate on cross-platform engines and not dedicate myself to any particular company or hardware.
I do understand the lure of the NDS and so I can't really knock it. It's just a shame that unlike most other platforms Nintendo doesn't seem to think budding developers are a valuable asset to have.