I wouldn't, really, but if you can't avoid it then the Complete mods are great. I've only tried SoC Complete, but I believe the other two Complete mods are of the same quality. They're basically graphical overhauls, but also include a ton of bugfixes and gameplay tweaks. Nothing over-the-top in my opinion - and the game still feels like Stalker. But again, I'd play through without mods, unless the bugs are really killing you (I somehow managed to avoid them completely when I played it...).
Yes. I mean, maybe I shouldn't have been playing it on Master difficulty. Either way, there was a lot I liked about it - I'm a huge fan of Stalker's gunplay, and it gave me a lot of that. I'd recommend it - but with the warning that it's the worst game of the three.