Ever have one of those days?
That's what went through my mind when I started playing Gravemind.
Halo 2 has other tough spots; the second hangar bay in Cairo Station, sniper alley in Outskirts, and Nothing But Jackal in Delta Halo. When I first played Gravemind, however, was the first time I backed off my intention to complete the game the first time around, all the levels, at Heroic difficulty or better. After banging my head against the wall that is the opening room of Gravemind, I restarted on Normal so I could get past the level and finish the game in time to write something about it before people stopped caring.
Most of the time in Halo 2, you've got a choice of weapons with which to face your foes, or recourse to go back somewhere and get them, or at least a place to hide. The audience chamber of Gravemind has none of these things. The only exit to the room won't open until you clear all the enemies, so you can't speedrun it. There are no areas that aren't exposed to fire from some angle-- and that includes the upper seating areas that Brutes will lob Brute Shot grenades into. When you start the level, the only weapon you have is a single needler, and the only dropped weapon available to you... is another needler.
UPDATE: I guess Gravemind is popular again all of a sudden, so I'm lucky posting at this precise time; Ducain at High Impact Halo has just made good on a promise to jump to the top of the level, the high building at the beginning of the outdoor areas after the marine rescue.