Shacknews has a post by Maarten Goldstein with impressions about the Game Boy Advance port of Doom. Overall he says that it appears to be a pretty faithful port, albeit with some limitations to be expected from the hardware.
The graphics are somewhat pixelated, but it still looks amazing. Its also not as fast as on the PC, but still pretty good. AI seems a little slower, probably due to the fact that you can't aim at monsters as fast due to controls. Besides single player support, multiplayer deathmatch is also supported. The fact that the engine is not as fast as the PC engine does affect gameplay in multiplayer somewhat since its not as fast paced, but it's still very fun.Also, he mentions that the blood is green, as I postulated last week. Oh well, hidden blood code perhaps? ABACABB anybody?