The Lin family invited me and my parents to their house for dinner, and I got to hang out with Moonway this evening. I'm very happy to say that I've finally beaten Ultimate Doom without cheat codes!
I had actually finished the original three episodes back in September, but I decided to take a break because the fourth one ("Thy Flesh Consumed") was supposed to be very hard. It was indeed quite challenging, but I still managed to complete it - although not without saving and reloading countless times.
You'll probably laugh at me for this, but I usually like to cheat my way through a game a few times before playing it normally. My rationale for doing so is that it lets me become familiar with the levels without having to worry about dying. This does kind of take away the fun, but it nonetheless provides good practice. To each their own, I guess.
I should mention that Moonway also recently completed Ultimate Doom legitimately. He says he's better than me because he finished the last boss with more health left. I guess I can't argue with that. :P
Currently playing: Ultimate Doom