The monsters have much more detail, especially close up. There are energy sources, which you use to reload your laser and advance levels, that just look like garbled blobs. Speed is a problem. Every time you move, the entire screen is redrawn, and this takes about 5 seconds depending on what you're looking at. The game is playable, though, because the levels are not the same size as in doom.
Loading takes awhile, besides the initial compile.
You can save your game. This game could use moving enemies, more variety, and a way to see enemies that are more than 2 spaces away. Having more than one weapon would be nice. It is way too hard. The enemies take forever to defeat, and at the same time they are firing at you.