In addition to all these great ideas there should be an overall feeling that no place is ever safe in the Zone. Mutants should be able to go anywhere at anytime (like a spot where a STALKER is taking a nap). And anomalies should change position about every day, say to get to Dark Valley you'll have to wait a day because anomalies are blocking the tunnel/path. It was kinda mentioned in vanilla SoC and CS that the Zone is always changing and that's what makes being in the Zone so difficult.
--ps. oh, and there will be random blowouts right? When a blowout happens it should turn your vision black and white like it was originally planned. I did that once to OL and it was very cool.