The other thing is that in the Halo 1 levels, you are fighting all the way, and the firefights could get drawn out. Halo 2 and 3 both have a sprinkling of enemies (even the Flood are not representative of their name anymore) which are dealt with so blindingly fast at any dificulty level that there is no game. It's run, blast, run. I can say that apart from Halo 2 Legendary, I've never had to sit and formulate a strategy for getting out of a fight in one piece in the last two core Halo games. ODST brought that element back a little bit for the Mombasa Streets, and that is what gives it its place in the series.