The Halo 1 and KOTOR twists do hit pretty hard if you somehow haven't been spoiled. KOTOR has one of my favorite reveal sequences ever with showing you how much foreshadowing you missed, and Halo's twist turns the game on its head.
You can only stuff about those games without having the twist or whatever spoiled. What Halo twist was it? I've finished it a few times and don't remember really. It was all about how open it was and the action, plus the multiplayer.
However, Reach's tagline was, "From the beginning, you know the end," so there was an expectation that everyone playing would know how it was going to pan out.