I've owned and played each Elder Scrolls game, Fallout, Fallout NV (including the originals). They've all satisfied my particular play style, some more than others, but always worth playing. If you looked at the games on my bookshelf, you'll notice there are few newer games (within the last 7 years) other than Bethesda games.
Oblivion has been my favorite so far. In fact, I bought a new PC in 2006, splurged $300 on a video card and $250 for a wide screen monitor so I could get the best visual experience. I'll be doing the same for Skyrim before it's release later this year.
I believe I've logged over 300+ hours playing Oblivion in various ways, including the Shivering Isles expansion. The bulk of my playing was for my heroic Paladin along with his trusty Shadow Mare, combing the land (no fast travel), in a quest to banish all evil by find each and every Oblivion Gate and closing them. I never got them all but it was fun nonetheless. I'm never in a hurry to "beat" these games. They are simply playgrounds.
Right now I'm playing the total conversion mod "Nehrim: At Fate's Edge"... which is unbelievably amazing btw.
The fact is, Bethesda Softworks games, especially Oblivion for me, have been the biggest bang-for-buck. For $50 or so, the game has provided unbelievable value in terms of casual entertainment. I'm still playing the damned thing 5 years later!
There are no other game companies that make open ended RPGs with the amount of quality, depth, and replayability as these guys.
At 41 years of age, I don't have the time or patience to play as many games as I used to, but I do however make the time to play theirs.
Regards
-pmanderson