The closet thing to Fallout, regarding the setting, would be "The Fall - Last Days of Gaia". Visual style is similar with a barren wasteland etc, too.
Whereas Deus Ex has a completely different visual style, as in lots of city, houses etc, and you are more in rooms, in high-tech buildings etc, as compared to Fallout with huge outdoor areas and many caves. More like always in Vaults/military bases.
And Stalker is an FPS, so not that much RPG elements, and it has pretty high requirements (well, today it isn't that big of a problem for a new computer, but back then..and i know many people, especially those who like story and nice visuals (as in looking appealing even years later, and not just (perhaps not even close) realistic. And it has less wasteland, too.
Not that "barren wasteland" is a must, it's just that there aren't that many games with the visual style of the Fallout games.
I also want to use the chance to recommend
Dystopia, a cyberpunk game (mod) for the source engine. All you need is Steam, which for itself is free, and Source SDK Base (which comes with CSS, Portal, TF2, L4D and many more games, as low as $4,99 if you don't have any game that gives you Sorce SDK Base yet) and you are good. Dystopia itself is of course free.
It's an objective based FPS, with three different classes, many maps and weapons, implants, cyberspace (hacking) etc. It also includes extensive stats tracking and a competitive league for all your nerdy needs.
Of course, you need to play it online (well, you can play it alone/lan, too, but whats the point...). The next big update with many bugfixes, some new maps and lots of updates to the old ones is arriving any time now, and it will become a Steamworks mod then, which makes a lot of things easier.
It's not that easy to learn, which keeps many people from playing it, but most people like to help you (there are not-so-friendly people everywhere, keep that in mind) if you ask and not just shoot teammates. And if you take your time, you can get into it pretty fast, and then it's lots of fun.
Of course, there isn't that much story, as you just can't do that in a multiplayer (unless it's coop..) setting.