Ultima 7:2 taught me more about DOS memory management than anything else. Had to handcraft a menu-driven autoexec.bat / config.sys monster to get that thing going. HIMEM.SYS ... oh the memories.
A single KB too much in a mouse driver and you were unable to start the game. Oh you want sound? Roland MT-32 or Soundblaster Pro? But how will you load all those drivers in those first 640K of RAM?
Shivers...