Doom is famous for being one of the most influential first-person shooters of all time, but would it have worked as a 2D platformer? Given the premise angry space marine must kill monsters, reach end of level it probably wouldn't have been as gamechanging, but judging by this fan project, it'd still have been pretty cool.
MiniDOOM is a "very short parody game" based on the first Doom, made as part of a course using GameMaker Studio. While short (it's only an 11MB file, too), it's worth a download just to enjoy the beautiful sprites the recreation of the Cacodemon is a personal favourite.
Download it over here, or watch the trailer below: