Have a look to the credits chart of oblivion...
What do you see there? Right a really great list of names, all working on that game for over 4 years. Famous publishers were spending a lot of money into that project as well.
Michael Schwarz is right, you might be able to do it with GS, but if you are alone and don't have 10 Million US$ to waste, you won't finish it in the next 40 years. Of course you can say: I am not talking about the dimension and grafic levels of oblivion just about the style and feeling of the gameplay, but then also think about what is making oblivion the game it is: Grafic level, and freedom of choice and movement. Both things, you won't achieve alone for sure.
But to many time for a lot a error (animations by sample)
I think is possible and make much better inclusive alone
but I need to go to the work or stay with my wife
if not with 12 hours at day or more
I think the publisher waste the money and the workers not work all the time in the production of the games
