I realized that the levels I hate in halo 3 and one (haven't played the second one.) Always have the flood in them. So I play the level that first reveals the flood (first game) it was fine not that bad but then they totaly flip their s**t with the next level. Do they infinitely respawn in some areas in that level, cause it feels like it. The hive in the third game feels simalir its just pure annoyance to me.
PS. playing Halo Combat Evolved on heroic. Also finished Halo 3 on legendary.