I wish my brain could tell you right now. For a few things: DTS audio, flawless opening crawls, greatly improved Boleyn sequence, various little changes, removed ‘high ground’ altogether, etc.
I would suggest getting V5 for archival purposes, since there will NOT be any further updates. But there’s not much to tout aside from ‘presentation’ aspects and little things.
V5 is the “Oh, all right, let’s go round one more time and make it as good as it can be before placing it permanently beyond my reach.”