The difficulty is nightmare (imp's fireballs and demons move twice as fast, monsters get resurrected).
You can enter cheat codes like normal. iddqd, idkfa all work.
It's running the shareware version of Doom 1, so no BFG.
Some of the keys like the space bar and esc are remapped, but a lot of keys still work like in Doom. Tab gives you the automap, shift makes you run, alt to strafe. Normally, you can get to the main menu by pressing esc, but since that got remapped, you can get to the main menu by pressing F1 to cycle through the help and ad screens before getting to the main menu. You can even select to restart Episode 1 and play E1M1 instead.
Destroying barrels count towards the kill total while monsters killed by exploding barrels don't count. Try to destroy the barrels in E1M8 (use idclev18 to get there). The kill counter only goes up 1 for the barrel even though you've killed at least 8 pinkies.
Rockets don't count towards the kill total. Try spamming rockets after entering id(k)fa. Your kill total doesn't change at all.
If you try to quit by pressing F10 and y, the game just freezes.
Here's what I found out:
The difficulty is nightmare (imp's fireballs and demons move twice as fast, monsters get resurrected).
You can enter cheat codes like normal. iddqd, idkfa all work.
It's running the shareware version of Doom 1, so no BFG.
Some of the keys like the space bar and esc are remapped, but a lot of keys still work like in Doom. Tab gives you the automap, shift makes you run, alt to strafe. Normally, you can get to the main menu by pressing esc, but since that got remapped, you can get to the main menu by pressing F1 to cycle through the help and ad screens before getting to the main menu. You can even select to restart Episode 1 and play E1M1 instead.
Destroying barrels count towards the kill total while monsters killed by exploding barrels don't count. Try to destroy the barrels in E1M8 (use idclev18 to get there). The kill counter only goes up 1 for the barrel even though you've killed at least 8 pinkies.
Rockets don't count towards the kill total. Try spamming rockets after entering id(k)fa. Your kill total doesn't change at all.
If you try to quit by pressing F10 and y, the game just freezes.
The quit messages include stuff that aren't in any released versions of the game.