Ok, I got Fallout 3 and I love it. I wouldn't call it a future version of Skyrim, it's the world as if the culture stayed in the 1950's, but then there was a nuke war (still, there is energy weapons), so it's mostly wasteland. A few bad things from Oblivion were fixed in Fallout 3, then executed better in Skyrim (e.g. lockpicking).
Most of the guilds in 3 you can't join, but they are: Brotherhood of Steel, Enclave, Brotherhood Outcasts, Slavers, you could call Mutants a faction, and there is another guild which I'm not sure of the name but you can find them by talking around Megaton (the first city you'll find).
As far as RP goes, NV is better for Hardcore Mode. To RP in 3 you'll want mods, but if you get it on a console you'll still be able to choose things like a merchant (follow around a trading caravan), wanderer (stay out in the Wastes), defend Bigtown (you'll find out about them later) and so on. If you want to know a bit about the lore just reply!
Characters to play are humans (Asian, Caucasian, Hispanic, etc.), but if you get it on a computer there will probably be mods for ghouls (humans that were a bit messed up from the nukes, look like zombies). The classes aren't really there, as you will probably use guns (big, small or energy) as there is not much melee and unarmed weapons. You level when you get enough xp (from killing enemies or doing missions). When you level you pick a perk (different to Skyrim as they are not in trees), and put points into a skill (e.g. mechanic, science, small guns, big guns, etc.) The points you get are determined by your Intelligence, which is decided at the start of the game when you pick your S.P.E.C.I.A.L, or Strength (how much you carry, and damage for melee?), Perception (enemies detection), Endurance (health), Charisma (prices, talking/negotiate), Intelligence (points for skills), Agility (not sure, gun damage maybe?) and Luck (critical hits, the useless skill). You'll have to look in a manual for the exact things.
You'll have to look for mods yourself, but there are swords in the game already!
I loved it, hope this helps you. One note though, if you get 3 buy the GOTY edition, because if you don't the game forces you to start a new character at the end of the main questline, instead of being able to do whatever you want afterwards!!!!!
