Things I liked:
Combat and encounters. You have a gift here - keep it up. There were some really nice surprises throughout and you tied the monster spawning to the story
of the level (Slipgate back online) which was cool.
For me, this was a really non-linear, interconnected place and I really never got too lost. You had some signposting to let me know where I was. As McLogenog said above - maybe make each area more distinctive. I always get lost in levels so this wasn't too bad overall.
Things that can be improved:
The button hunt was tricky. This could have been bad. Some of the buttons were pretty tricky to see but others were cleverly placed so as to not miss them. (the gold one was easy at least!)
Some other things to consider:
The player can get stuck in a few places on brushes that stick out of the walls. Make sure and use clip brushes here.
Button animations are mostly off in your map. Check this out to avoid that: https://youtu.be/xnSqmHOh3XQ?t=257
Keep making maps - excited to play your next one!