Stylistically, this is one of the best games in the jam. The intro cutscene sets the tone perfectly, and I think it really fits the retro style of the game. The enemies and sound effects are really good, and really helps to create the impression of an early doom mod.
Unfortunately, I played the game 5 times, and could never complete the boss with the chaingun. This was mainly due to a bug, which prevented guns from firing. For example my shotgun suddenly stopped working halfway through my third playthrough, meaning that by the time I had reached the final boss, I did not have enough ammo to defeat him between my other two guns. I had a similar issue with my pistol in some playthroughs, and also had an issue with the chaingun which meant that when you switched away from it, and back again, it would sometimes lose all it's ammo. Because of this, all of my playthroughs ended at that point (The restart button didn't seem to work either so I had to close and restart the game each time).
That said, with a patch to fix these bugs, this could be a really strong contender. I really enjoyed playing this game, and you should be proud of what you did. The style and theming carries this game a long way, and you should be proud that you (almost) finished the game on time. A big well done!