There is modifigation wich allows run Blood wad with doom engine, that would be nice. Blood is really good game with scary athmosphere.
http://en.wikipedia.org/wiki/Blood_%28video_game%29
It migh not be true, but anyway build engine would be nice and playable even with AGA.
http://en.wikipedia.org/wiki/Build_engine
AND it would allows games like, duke nukem, shadow warrior, witchaven 2, redneck rampage etc. tens of games.
There is already nice ports of doom and quake for 68k amigas, I do belive that you could do better, but do they offer anything new?
http://www.dmoz.org/Computers/Progra.../BUILD_Engine/
http://advsys.net/ken/build.htm
Sources are available