I was never even all that impressed with the original Halo, to be honest. It was a solid game, and the overall storyline/setting was fun (fantastic soundtrack too), but there were some glaring problem areas. While the singleplayer campaign had ten levels, they comprised only five legitimately-unique locations, and most of those had a massive amount of architectural repetition within them. (Dear lord, that assault on the control station...) The combat tended to evolve into a very repetitive pattern of strafe-from-cover, fire-a-few-shots, and duck-into-cover-to-recharge-shields, and the relatively-few enemy types didn't mix things up all that much. I only played multiplayer a few times, but the whole thing felt very slow and ponderous gameplay-wise, and I usually wound up getting picked off by snipers from halfway across the map before I made any real headway. I started out as a Descent player, so I guess I was just much more used to Descent 3's fast-paced 6DOF style; I guess the equivalent FPS would be something like TF2 or UT.