Spoon, are the Stalker games real RPGs, or more of an FPS? I've heard they may have some RPG elements, if so, I'd be interested in them myself.
Focusing on the first one (which is the best of the three), you play as a STALKER (groups of ex-military, mercenaries and fortune hunters - of artifacts and myths) in the forbidden and radiated region of Chernobyl following a nuclear meltdown. You are trying to piece together why you are supposed to kill someone and at the same time find out about the strange things happening in that region and other myths.
It is open world (or semi-open world) as you travel from large region into another. You speak to NPCs to get missions. It is non-linear, and you can follow the main quest line or the many side quests that you get from NPCs for a reward (money or kit), and there is no hand holding. There are also shops to buy and sell things, and you can also trade with NPCs. Moreover, there are certain events that you trigger in maps, which makes the world feel dynamic. There are many ways to approach missions (sneak, brute force .. etc.).
There is no leveling up but there are stats! You can find/buy/trade weapon and armour upgrades to boost your stats and kit, and more importantly there are 'artifacts'. These you find all over the map (some are easy to find, and some are damn hard to find or to get) that you can equip to change certain stats (e.g. boost armour but reduce radiation resistance, increase fire and radiation resistance .. etc.) and these are stackable.
Combat is through first person, there are many different types of weapons and weapon upgrades to improve weapon stats (recoil, zoom, .. etc.) and it is one of the best. Enemy AI is also one of the best that I have seen as well.
There are also survival elements in that you have to eat food and use anti-radiation injections as you are bound to be affected by radiation. There are also factions that you can join.
The atmosphere in STALKER is one the best that you can find in a game. Mixing horror, uncertainty, despair, helped by the dynamic weather and certain forbidden regions in the map where there are radiation storms or incidents. The lore is very rich told by NPCs and scattered letters (and dreams!).
So to answer your question, it does have many rpg elements (stats, quests, nonlinearity, factions, and loot).
You can find the first one as a disk version cheaply on eBay (which you can then claim on GoG)!
