The problem in Stalker is the "equipment levelling" system, where every gun you get must be progressivelly better than the last one, in order for the system to work. Since there is no other levelling scheme, this is the only thing that makes stalker RPG-ish.
Which, I think, isn't necessary. I would for one would gladly trade the "dozens of guns" model for a "few guns, each with their own character". Implemented properly, it would work wonders. Of course, to model some of the guns properly you would need some sort of a "handling system" - that is, some guns would be prone to breaking if you handled them roughly. Otherwise, the AK would not be the AK we all know and love, but just an assault rifle with cool looks and somewhat clumsy sights.
Just what "rough handling" would mean gameplay-wise is up to discussion, however. If it worked this way, though, players could choose guns based on other factors than "damage, accuracy, scope, silencer?"
Equipment levelling could still be done with gun mods, attachments, customization. How cool would it be if you could repaint your AK into a camo scheme, for example, and duct-tape a camping flashlight to it?
All in all, most assault rifles (and pistols and SMGs for that matter) should be roughly equivalent to each other, with their own special quirks, and appearing throughought the game at the same time. I long for such a system to be implemented in at leats one game during my lifetime
Oh, another gripe with stalker: pistols are fucking useless as a backup weapon, if only because your character has to
rack the slide every time he pulls the pistol out. The whole point of a backup weapon is that you can pull it out fast when your main runs out and unload an entire magazine into a bloodsucker that's about to tear your face off! But because of this single animation, pistols become orders of magnitude less useful.
Also, they can't be replaced with shotguns later on. Which, needless to say, sucks dick, since I only carry a rifle and a shotgun now and have to swap them out manually.