Long ramble of early impressions: The visuals and engine. I find them excellent and they run well without lag problems even in big fights. The anomalies look great and sometimes make for good puzzles. The combat against man and beast so far is fun and reminiscent of the Hitman games for me, but it does need balancing and tweaking. The AI can sometimes be a joy in combat when it seemingly starts flanking and sneaking on you (and not committing suicide by walking straight into an obvious anomaly). The atmosphere is great, it feels like I am in a post-apocalyptic environment and for the most part the immersion in that isn't being broken. The way the NPCs wander, talk and play guitar by the fire are all similar to the Gothic NPCs too.
The counterbalance to this is the AI sometimes doing colossally stupid things, the respawning waves of bandits and other enemies (sometimes right in front of you where it is jarring), various random bugs of the mundane sort, impossible or too tight timing on the quests (I've "failed" a few quests because I was forced to walk miles to the other side of the map to get the reward for completing the quest. That's right, even if you kill the big foozle within the 24 time limit you have to come back and claim it or you take the hit as if you failed completely or didn't even bother. Same with retrieving items for people and such, so you might arrive five minutes late with some treasured heirloom that someone has been looking for for ages and then be ignored as the quest has officially failed. Sucks. Sometimes the quests are generated for areas you cannot get to fast enough yet because of the plot or sheer distance and so on and you have no indication of these before accepting, sometimes these random quests are forced on you without you having any say in the matter too. I had one happen where an outpost broadcasted an open request to all free Stalkers around for help against an impending mutant attack, I ran straight there but every time I was too late and the people at the outpost easily wiped out the attack and I personally was contacted and had heaps of abuse poured on me by the local leader of that faction, despite the fact I didn't choose to accept the mission and it wasn't directed at me in the first place. This happens whether you are at the other end of the map for the duration or in the outpost at the time. I tried reloading it several times, but I was simply too far away to get there in time to make a difference. Sucks.
The middle ground where it is debatable would be the carry limit and the lack of traders, by that I mean that I'd like it if the average Stalker would be willing to buy whatever you had, even if it was a less favorable exchange than the true traders it would work fine for me. As it is all the Stalkers don't want anything but consumables and artefacts. I hate having to load up on a couple of guns and then spend hours walking back to the trader while wheezing like an asthmatic. Same goes for trying to salvage special items.
It's early days for me yet, so my opinion might change or I may discover some aspect, but I'd love it if there were vehicles to speed up the dull journeys, even if they were in game terms "teleporters" like the town to town travel in Morrowind. The combination of long walks and too-frequent respawning makes for an irritating journey and all the harder to store any loot you have - especially the unique or rare loot like weapon upgrades and so on. Being able to hire people into a squad as backup or pack mules would be great too, but maybe that comes later on. The shops could also be a lot better as right now my vast wealth seems useless. The economy seems broken in that I have heaps of items to sell (so much so in that it is a chore and seems increasingly pointless to gather loot), but nothing worth buying as I found the best gun so far lying on the ground, the traders sell tiny ranges of items and they are rarely useful. I was also given the best armor I can find so far as part of the plot (after spending ages looking for some and only getting a slight upgrade). I know there are several suits of armor in the game that they could have given me or made available, but I was forced into wearing this shitty leather coat I got at the start for ages before leaping ahead to this Stalker suit that blows all that other stuff away. It should make available the more gradual upgrade cycle so you can spend some of that money, where are all these other people getting all that equipment otherwise and why are they bothering to gather that money if it is useless?
If you like FPS combat and the Gothic games you probably would like it more about it than dislike. I know it can't be all that bad as I haven't quit in frustration despite numerous random deaths.