jDoom is pretty awesome. I play it in linux. On my Amiga, I usually play ADoomPPC. It allows resolutions up to 1600x1200 and runs rather fast. It even gets better than 20 FPS in AGA. A video card is recommended though. :-D
I don't know if the improvements in ADoomPPC were ever back-ported to ADoom for 68K. jDoom would be nice on the Amiga, but it would need hardware 3D.
