Calling Red Faction a Half-Life clone misses the point entirely. The game was originally created as Descent 4, but certain legal issues (the details of which I am not clear on) forced Volition (the development studio, who also created Descent: Freespace) to scrap that idea. Certain aspects of a Descent plotline remain: the mining theme, a flying ship you use at points with abilities not unlike Descent's PyroGX, and other things. The Geo-mod engine makes incredible sense as one for a Descent game (where the basic premise is "mining bots go bezerk"). The fact it's a FPS seems more than a little odd, though, and I'm almost glad that it wasn't Descent.
This makes even more sense when you consider the weakness of Red Faction's plot: when Interplay (owner of the Descent franchise) yanked the license, Volition must have been in a hurry to come up with a new plot, thus the very simple oppressed-miners-revolt setup in the final game.
Alas, though the game is a very passable first-person shooter with some unique elements (such as supreme drivable vehicle support), it will not be remembered as a classic.