Biggest disappointment for me is the intentional handy capping of un-patched games. I knew this ahead of time but locking un-patched games to older specs is still disappointing news. Seems the UI and boot time of the system is the same too which is also disappointing. As a primary PC user having games that had frame rate issues in areas cleaned up with better hardware would be really nice. As would getting into the menu faster to join a party or send a message mid game. Boot times being quicker would be a bonus but not a big of a deal. Little things that Sony could have done to make the Pro even better were ignored for "Compatibility" even though the Xbox One S handled it fine.
Xbox One S doesn't have faster boot times or anything of the sort though, because it has the same HDD and general hardware. Also, the improvements to games are few and far between, and don't happen for most titles because the GPU upclock is very small, which is why MS allowed it.
Xbox One S and Pro are offering very different types of functionality.