What kind of RPG are we talking about? RPG is one of those things where every single person kind of has their own personal dictionary of what an RPG is.
But, since I'm not really in a great state of mind to get into some huge argument about it, I'm going to have to say that Fallout: New Vegas is probably my favourite RPG, if not my favourite all around game of all time. The plot is great. The characters are great. The freedom you have to resolve quests in different ways is fantastic. The stat-building is really rewarding. The companions are memorable and interesting.
The only other game I can think of that even came close to giving you so many choices and so many different ways of playing your character was Dragon Age: Origins, and even with all the different options that game gave you of killing off potential party members, siding with the bad guys, and all the different back stories and relationships you could have, I still don't think it comes close to the sheer variety of different ways you can play New Vegas. I honestly can't believe I didn't like this game the first time I played it, because, now that I seriously took the time to play it, I have to say it's probably one of the best and smartest games I've ever had the privilege to play.
Basically, if someone combined Fallout: New Vegas with Dragon Age: Origins, you'd probably have my perfect game.