Want a whole new experience? Beat the game on Impossible difficulty.
I just did that a few days ago, it felt like a whole new game after beating it 3 times on "Normal". Impossible difficulty is ridiculous, especially if you don't play it "right". Hint: beating it on Impossible is a LOT easier if you only use the Plasma Cutter, as you'll have a good amount of ammo for it. Trying to beat it with 2 (let alone more than 2) guns makes the game a hell of a lot harder because you'll be constantly running out of ammo.