Voice acting isn't really anything to do with the engine, more to do with the fact that Oblivion had 12/13 voice actors in total. (Unless you mean the voices changing mid dialogue tree, which was horrible indeed, but not necessarily an engine constraint.)
Example - Jonathan Bryce: Argonian, Khajiit, Nord, and Orc males, Molag Bal, Hircine, Malacath
Last I heard - Skyrims voice cast is 70+ strong, so it should be noticeably improved in that regard.
I didn't have any issues with the physics in Oblivion so unsure what you mean by that. The pathing & ai in general will be a mixed bag undoubtedly.
None of that is especially a big deal to me though, I can easily look past it, my only concerns are PC related, or horrible game breaking bugs.
And cash cow? The last Elder Scrolls game released almost 6 years ago.