The stalker games are amazing if you can get into them, and they have one of the most dedicated modding scenes around (several!). I have played at least three mods which radically alter the game, where they feel more polished that one of the stalker games itself! So while you can get to play three very interesting and fun games (there's three in the series), you can go a whole step beyond that and increase it more to, like, 6.5 (at the very least) games due to mods. Complete games, mind you.
With such an easy dev kit available for many Bethesda game, pretty much any Elder Scroll game starting at Morrowing, and the last two Fallouts, will have pretty interesting and useful mods. Most of them will augment your experience to even better grounds, and a few will provide new content that's highly enjoyable.
