I'm downloading (so very very slowly) Lost Alpha, I'm very much looking forward to playing it. The original STALKER and CoP were two of my favourite games, dripping in atmosphere, specially once modded with various asset improvements.
I'm interested though why you stuck with the original SC engine rather than the more recent, and I assume more advanced, CoP engine? I have no doubt I will enjoy Lost Alpha whatever it uses, so don't take this as a "complaint" about the engine, I'm just interested what the SC engine brings that the CoP does not. Maybe my assumption that the newer engine is better is wrong?
What I do remember is that playing SC even on modern hardware suffered some very very annoying loading/asset-streaming issues causing horribly annoying stuttery game-play at times. I actually resorted to running the whole game off a RAM disk at one point, and it still didn't totally fix the issue! So if that issue is fixed/not there, that's a big win right off (although CoP didn't suffer this issues at all).
I also remember the maps being a lot smaller in SC, with many more loading points (breaking immersion to a degree). Is this something that has been changed in LA?