I really want to make a game using a software rasterizer sometime - just to prove its possible. Back in the good ol' days, I had to get by on my dad's PC, which had no graphics acceleration, but a farily substatial Pentium 3 processor.

Games like the original Half-Life, Unreal Tournament 2004, etc. ran surprisingly well and at decent resolutions.

With the power of modern hardware, I guess you could do a decent FPS in pure software with even naively written code, and not having to deal with the APIs, but having the absolute creative freedom to say 'this pixel is green' would be liberating.

Fun fact: Due to the divergent nature of computation, many ray tracers targeting real time performance were written on CPU, even when GPUs were quite powerful, software raytracers were quite good, until the hardware apis started popping up.