I said it a few days ago and I do it again: Gloom-based total conversions are fashionable lately and so is P. Rex' project Pharex: The Second Invasion. It's a Doom 2 total conversion based on hi webcomic series, Poharex, which will celebrate its 10th anniversary this April.
"In this game, you assume the role of Poharex, a heroic dinosaur who must defend his primordial jungle home from an alien invasion. These aliens did not arrive from space, but from within an ancient, abandoned city hidden deep within the jungle, and Poharex must survive the long journey there to eliminate the alien threat once and for all. You start the game with no weapons other than your powerful jaws, which you use to crush your enemies to a pulp. Later on, you'll find out how to use the Thumos -the aliens' power source- to turn your roars into powerful energy blasts."
Sounds crazy? It definitely is. You can play a first gameplay demo by visiting the thread and downloading the piece. Take your time, there are a lot of screenshots and additional information you can take a look at while the download is running.