Apart from the UI, Reviewable also handles many of the really ugly "they did an over-under rebase, force-pushed, did another, then flipped back" cases that come up with longer-lived PRs and manages to keep the review state reasonable better than any other tool I've seen. And we've tried quite a few of them :-)
* /reviews page takes around 5 seconds to load
* Sometimes the above page gives API rate limit exceptions
* The list of PRs on the above page are not wrapped in an anchor tag. I can't right click the links (to open in a new tab for example), I have to hold onto cmd and press a small icon instead
I love all the features you offer, but the UX is not very pleasant at all. We can set up a web session to show you more of my experience.