Keeping the user in their editor for code reviews is pretty nice indeed, but I think that with larger projects and bigger changes, it's going to be way more difficult to skim through what has changed where, which helps me identify how to start reviewing. There would have to be an easier way to see what changed where quickly without having to mess up my working tree (which is almost always dirty with something) and having to stash or switch back and forth between branches for reviewing is going to be painful. Sometimes I have small comments or questions, I'd like to be able to do that without having to download the entire patch.
Also, I'm not sure if I missed something, but does every review get applied as a commit by itself that I (as repo owner) would have to squash? This feels like a chore by itself.
I have relied on github for previous work but for the last couple of years I've been primarily using Gerrit for my job, and although there are some drawbacks, I absolutely love its workflow. Github workflow is not free from drawbacks either, and if I'm asked now I absolutely prefer Gerrit's to Github's. Gerrit uses Git references in a unique way to facilitate code reviews and patches (which consist of one or more patchsets). I rarely use branches now except for extremely long-lived experiments, or for local temp purposes. A patch gets merged as a single commit no matter how many rounds of patchsets the submitter adds and reviews they get, and when needed I can quickly download the patch at any patchset to a different branch and then delete it.