JLF65 has updated his Doom port for the Dreamcast.

Changes:

Latest version… fixed a problem where it would wait on input that never came when you selected a patch wad. Patch wads should now work fine. I went ahead and included my favorite Doom 1 patch wad: Doominator. Note: you need DOOM patch wads, not BOOM patch wads. BOOM pwads may work to some extent, but not fully as this version of Doom is based on DOOM, not BOOM/PrBOOM. You also need the full version of Doom or Ult Doom for Doom 1 patch wads, and the full version of Doom 2 or Final Doom for Doom 2 patch wads (not included).

http://dcemu.co.uk/dcdoom-v1-1-4-233890.html