Overall I really like this level, and it's great improvement from your first one too. I have some suggestions for improvements that occurred to me while I was playing:

The repeated horizontal grav lift walkways seem pointless and boring since they just kind of link into each other right away. I think that section would be better if they were spaced out a bit more, or just cut down to a single walkway.

I shared my thoughts on the reactor in the other thread already, but just to summarize, the reactor needs to be more clearly something that's supposed to be shot at. Try decorating it like things we're used to shooting at like energy shields, instead of just another piece of scenery, and have it react to shots immediately to reward that behavior, like with shield flares.

The ending escape out of the ship would be a lot more interesting in something fast like a Ghost or Spectre (with the ceilings so tall, maybe even a Banshee would work), rather than a slow Wraith. You've set yourself up a great opportunity to do the equivalent of an end-game Warthog run, and you can even still link it up to your current ending of boarding the Pelican (like Echo-419 in the first game, except they don't die)