Ruins: The placement of chests is much better, but the ruins don't look like homes of the ayleids at all.
Forts: Done pretty good. Except for the unlogical chest placement.
Oblivion: Very well done. But the sigil towers could've been much more different.
Houses: Yep. The real evidence of copy paste.
But the biggest con is the lack of variety of the looks. I mean, it is always the same wall, same floor, and you always see the same rooms(in caves for example).
Skyrim pretty much did it nice. Some nice views, more meshes and textures for the dungeons.
But I never understood why they didn't do it in Oblivion. If I was a game dev, I wouldn't be happy with it. They only needed to add some space, and add a few new meshes for the caves. Skyrim only had 3 types of caves IIRC (Spider, Natural, Excavation) . The worst is, they succeeded to do this in the Mehrunes Razor and SI DLC. It's not that I'm complaining but I just want an explanation, with a reliable source.