STALKER is a fantastic game once you understand the nuances. It also has a great mod community but I suggest playing through at least once vanilla (unmodified).
It doesn't hold your hand though. Prepare to really break in the quickload button.
STALKER NEWBIE GUIDE (VANILLA EDITION)
I keep dying in combat!
STALKER is not Halo. Find cover, aim (right mouse), go for headshots (on enemies with heads). Use Q and E to lean around corners. Move slowly, listen for enemies, and stay frosty.
I can't hit anything!
The beginning weapons suck, especially when firing from the hip. You might have better luck grabbing a shotgun and getting in close. Trying to 'snipe' with any unscoped gun will get you killed. About 1/3rd through the game, you can start grabbing scoped rifles which let you engage from farther away.
I can't run very far!
Find artifacts that up your Endurance. Eventually you'll have almost limitless run. But no amount of artifacts will prevent you from getting tired if you're overweight.
I'm always out of space in my backpack!
Once you get a solid rifle, drop your handgun. Anything that can't be taken down with a full rifle mag is only going to be annoyed by pistol rounds.
Try to trim yourself down to two primary weapons and stick with them.
Bread is lighter than rations or sausage and does the same job.
Antirad is lighter than vodka and does a better job. It can also be easily looted in the field, so don't feel the need to carry more than 20. Same for bandages and medkits.