I did this on my Family RP. Discovered most of the hidden areas and one easter egg. Some reason I don't like the Area 51's textures. My people hated it because it was glitchy. I suggest retextures, lots more building enterable, make the airport larger so planes can take off, and enhance that brick house's textures and make it a tad bit bigger. This is now one of my favorite maps. This feels like GSF.
Other then those, great job.