I have to say that STALKER RPG is one of the most evocative and superb roleplaying books I've read since I started gaming (over thirty years ago now). I'm unashamedly old school, and so have no real interest in the FLOW system per se (ok, I'm probably missing something, but that's just me). However, STALKER is very rules lite; only a small proportion of the book is given over to rules, the rest is background presented without any game stats.
Thus, STALKER RPG, being mainly a (generic) background book, presents no problems in applying the material to any major dice-based system (BRP, D20, GURPS, Savage Worlds, whatever). So, for those who may be hesitant about the FLOW system, don't be. Get the book and apply the beautifully pitched background to your system of choice.
[5 of 5 Stars!]