This is great wargaming inspiration - the setting is the devastated Cheronbyl radiation zone. Exploring the ruins, avoiding wild animals, mutants, bandits and fellow explorers (stalkers). There's a story with lots of quests and secrets to unlock, but besides the moody atmospheric world (which is divided into 3 "open world" stages), there are two main points that make it stand out:
(+) You feel like you are part of a living, breathing world. Many games you know the NPCs are standing around like dummies, waiting for you "the chosen one" to walk up and initiate a dialogue option. In STALKER, NPCs move around the map; you may come across random battles between bandits and stalkers - they act independently of you.
(+) There are no stats to "level up." You can improve your gear, and your personal knowledge and aiming skill, but you'll never have a level 50 character effortlessly 1-shotting a level 2 mutant boar. You need to actually be able to aim, FPS-style, instead of just tabbing or reaching for function keys. If you can't aim down iron sights, you're screwed, no matter what uber weapons you own. Gear makes a difference - getting my first night vision goggles and starlight scopes made me feel able to explore at night, rather than fleeing indoors the moment dusk began to fall. When I traded my rusty AK-47 and PPH pistol for a silenced SVD and a SPAS shotgun, I felt more comfortable initiating fights.
Conclusion: With its moody, creepily atmospheric maps, STALKER:Pripyat has a real survival feel. Having player skill and knowledge instead of relying on your "level" gives a real feeling of achievement. As "gearing up" is the only other way to improve, discovering a cache of ammo for that rare sniper rifle is an exciting find. If you like it, the original, STALKER:Shadow of Chernoybl is less polished but much more hardcore - you'll find yourself dying far more, and establishing food and ammo caches all over the map in a vain attempt to stay alive. The main downside to this series - it's single player, and the graphics are not exactly cutting edge.
M&B has a bazillion mods - from LOTR to ACW, Napoleonic. There are two official mods - for the viking era and the "Fire & Sword" Polish/Lithuanian era. Again, the example video is horrible but ****ing Blogger must only allow you to link to paid Youtube sites.
MOUNT & BLADE: WARBAND
This RPG is an acquired taste, but offers a unique gaming experience. Most RPGs offer "freedom of choice" but you really end up with only 3 endings - the good, the bad, and the neutral ones. So you are "free" but only really have 3 options. Other open ended sandbox games (like Grand Theft Auto) which have no real objective, tends to results in players mindlessly blowing stuff up or grinding for weapons, without purpose. In short, most game offer either the illusion of choice (whilst funnelling you into only 3 actual results) or meaningless choice (you have total freedom, but no meaningful impact on the game world).
(+) Mount & Blade is I think is unique in that it is a "meaningful sandbox." Every decision you make alters the game. You decide what your own "ending" will be - and you can change your mind as you go. There is a huge world map to explore, which you move in real-time as a "party" icon. You can visit (and raid) castles and villages, encounter raiding war parties and bandits as well as peaceful (but lucrative) caravans. Once you enter a location, you switch to over-the-shoulder cam and can organise your troops (up to 200) in a freewheeling fight - a bit like the way the Total War series works. There half a dozen factions, each with more than a dozen noblemen - each with their own armies and agendas. Some are cunning and treacherous, some are noble and honest. Befriending some may along you against others. Factions periodically declare war on each other, further muddying the waters.
Social skills actually matter. In most RPGs I eschew these - why stat up a boring "conversation" skill which is only rarely useful, when you can sneak in and steal what you want or simply kill them and loot it off their corpse? In M&B, I carefully cultivate relationships, and care about how persuasive I am. Have only a 20-man war band, but covet that castle? Fine, if you're persuasive and popular you might talk three other barons each with 100 men to help you out in the fight. And then you might come out on top when you divide up the spoils. You might marry into the king's family - or get elected field marshall of a faction. I once won a war for my faction by incarcerating every noble on the other side in my dungeons - leaving them leaderless.
Found the pretender to the throne? Why not instigate a civil war? The new king should be grateful. Want to become king yourself? It'll take many battles and much manoeuvrings to get there - but then you'll need to stay there and keep everyone happy (or at least, the people who matter.)
(+) The combat is very good. Mount and Blade's ability to direct sword thrusts and slashes with a flick of the mouse has ruined me for all other RPG combat. The ability to feint, and direct your blows is originally awkward (i.e. you miss a lot, as you are used to being able to simply spam buttons rather than think about where you are hitting and timing your swings) but soon feels fluid and natural. Mounted combat is also a staple (rather than being added as an afterthought); although feels a bit overpowered at times - horse archers are impossible to pin down and knight tend to flatten anything in their path.
A word of warning:
Mount & Blade: Warband is very much a "diamond in the rough." The graphics are.... ..."old school" is to put it kindly. The game seems very empty. Cut scenes are non-existent. If you are used to the game leading you by the hand (Mass Effect-style) and you want to be told a story, you will hate it. In Mount & Blade, you have freedom to create your own story. You have to decide what you want to be, and work towards it. NPCs do not run up to you hailing you as the Chosen One and offering you quests. There is no helpful arrow towards the next quest or waypoint. There is no epic overarching story. You start as a random warrior with a rusty sword (prey for every bandit group) and you work your way up to be whatever you want. You can leave a mark on the open world, through your battles and relationships and land holdings - and your ending will actually be what you decide it will be.
If you are tired of "vanilla" RPGs and MMOs, I think STALKER and M&B are well worth a look.