What I miss at github is a single view that list all the commits in a pull request, in sequence, with both commit messages and diff contents, with possibility to comment both message and diff. Oh, and have the commits show in the actual order the commits will show up in the history.
Github has certainly come far this last year, but these are all oh so simple and basic stuff.
I haven't used Gerrit in a few years though, maybe it's changed.