I've been checking out the Game Boy Advance version Doom yesterday and today and figured I'd share some impressions. Of course, it's hard to give any info about Doom itself that you don't know so I'll just keep to impressions of the port. Technically, it seems pretty damn impressive. It's Doom in a tiny machine. It's about as faithful to the original as you can get. Some levels are slightly (really slightly) different but all the weapons, items, sounds, music, monsters and even level transition screens are there.
The controls are about as good as they can get on a small machine like this. The normal control pad is used for turn left, right, go up, and go down. The shoulder buttons are used for strafing, B is used for opening doors, and A is used to shoot. Weapon switching is done by pressing both shoulder buttons and then press up or down. If this config is not to your liking, there are 5 other configs. You can't remap keys yourself. Obviously its not as good as a keyboard, but it works well enough.
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.
Besides sometimes slight level changes, the other change compared to the PC version is the fact that the blood is green. Yes, corpes lay around, but they're green, instead of red. It looks kinda weird but its understandable seeing how they could score a Teen rating this way.
All in all, as was always the case with Doom, it's a great way to spend some time if you're travelling, especially if there's some one else you can deathmatch with. There doesn't seem to be a release date for the game yet, but the version showing at QuakeCon seemed pretty much complete.