So, this independent homebrew game, Halo Zero (PC), is pretty fun.
Take the concepts from Halo, and Halo 2, and mix it in with side-scrolling 2D Contra-style gameplay?
In the words of the current Guinness marketing message: "Brilliant!"
It's not perfect; the game's died a few times, and though I laud the implementation of the Halo-favorite sniper rifle, the implementation sucks (there should be one button for zoom, and one for fire; as-is, you wast bullets, and disrupt the pacing of the game).
But, overall, a great romp for a few hours, and a good addition to the Halo universe.
Go to the website (www.halozero.new.fr/), download the game, and have fun, Halo-cum-Contraesque style.