Blackmesa is actually very linear. Everyone is moving in a general path in cramped spaces, the only exception is point A. You really have to know the map well, and the flow of people to understand what to do.
In stock maps, you have many options to flank and places where there isn't a lot of players that you can go through. Also, since blackmesa is fast respawn, it makes spying even harder since there is never any empty space to use.
I guess so, but if you do know the map like you said, its pretty easy. Even if it is linear there are plenty of bumps and stuff that you are able to stand on (That little crawl space to B or K, you can stand on top of it from the entrance.), Most spies usually hang around A, but it is a pretty easy map to spy on I think, or at least better than 2fort. But From all the eGO servers i think egypt is the easiest.















oh, and don't forget to disguise 



