Git-code-review: using Git and GitHub for daily code reviews
blog.lunarlogicpolska.com
blog.lunarlogicpolska.com
In my team we usually do on-demand code reviews via GH pull requests (though we don't merge them with merge button, rather manually to have flat history), I wrote a userscript to facilitate that in case the commit is lengthy [1]. Works with Firefox+Greasemonkey or Chrome+Tampermonkey.
Besides, even with feature branches I try to review things early instead of waiting for a pull request sometime later and then commenting "oh no, it's all wrong"...