You'll love fallout 3. As mentioned above, get the "Game of the Year" (AKA GOTY) edition. You didn't mention Morrowind... so get that as well.
I would also recommend the Fallout Trilogy (Available in a set, with Fallout 1, 2 and another in the fallout series. Fallout 3 is not in this). You'll probably spend about ~$60 on all that, and you'll get at least as much play time out of it as you have with Oblivion and Dragon Age combined (but probably more). Do you have the expansions for Oblivion?
I don't recommend Fallout New Vegas due to its incredibly intrusive DRM software, which requires online activation through Steam just to play it, even if you don't purchase it through Steam. Plus it requires you to go through Steam for updates, and other things as well. I returned my copy for a full refund because of all that BS. As for the rest of the fallout series (or ES series), though, they don't have any overly intrusive DRM or other ridiculous requirements and I highly recommend them all.