I don't think these difficulty levels differ a lot from each other. On easy, it auto reloads and uses the healthpacks automatically when your health reaches critical level, on normal it only auto reloads, and on hard it doesn't do either of these; another difference are the facehuggers who move a lot more swiftly. However, even on easy the game's extremely hard. I had to play it two times, one time I've gotten to level 7, but I had no ammo left for any of the fancier guns, and I couldn't progress further with what I had...so I was forced to restart and then I learned you could break the crates with shotgun or pulse rifle, as well as developed a habit of conserving ammo. I think I beat it on normal difficulty setting.