This level I really like. Huge open spaces to start with after the claustrophobia of T&R. The beach is a headscratcher - it appears to go straight, and yet you get to the same place in both directions. Some scary ass Blair Witch style stuff going on there.
As such, you can also skip straight to finding the security room, rather than finding the locked door first. In fact you really have to to make the par time, and it's much easier when you're going for the pacifist achievement also. No shooting, grenades, melee, dying or restarting. The two go well together, and at least you can do them on easy. The escape section really does feel urgent then.
The way more enemies appear throughout the complex after you see the map cutscene really annoys me. While it was incredibly contrived, I far preferred M2/Moo's style of enemies teleporting in nearby only. It at least made vague sense; the covenant just appear from nowhere, everywhere. And finding the way out from down there is a right pain! I'm reaching the end of the Halo 2 campaign, and it -was- going so well, with shorter, more interesting and varied missions, but now it's back to copy/pasted segments ... to the point that I'm not sure if I'm progressing or going back the way I came sometimes. The lack of a map still really sucks. There's some kind of irony that this was the map room.
It is also amusing that you can force the warthog through enough gaps to get it down to the security room. Which was one method for getting the 'skull' down there, involving grenade jumping, which is much more difficult than it was in Marathon, mainly because we can actually jump here, and the timing of it is really important!
Abysmal drop-offs are for some reason built into a lot of structures in the Halo universe. It seems downright inconvenient to me!