Well there are a lot of versions of the site. There is the "old old" version (back in the days of friends instead of follows) and there is the recent changes where we lost the split-view of answers in return for... for nothing?
If you mean the "old old" version, I like the highly customizable live feed that this one has. I think that is the biggest feature worth retaining.
If you mean the "old" version as in the last update, then I would like to see the split view returned.