I've been using GitHub for code review (both open-source and commercial projects) for about 5 years. It's improved a little bit, but for PRs with >100 files changed it's obviously lacking good UX.
For me, the biggest improvement would be the tree-view you get in Fisheye/Crucible. It's so hard to get a grasp on large refactoring PRs on GitHub.
This extension [1] makes code reviews more bearable, I highly recommend it. I don't understand why Github hasn't shipped this years ago. They've been improving the UX since their acquisition but there's still a long ways to go.
I wonder how one does manage a PR with >100 files changed. I realize these are sometimes unavoidable, but shouldn't we strive for smaller PRs? No tool will help you with exploding complexity...
Usually with massive PRs of that sort I’ll have several smaller PRs to a separate branch that get reviewed so that everything in the massive PR to the main branch has already been reviewed and the big one is just a cursory look. But this approach probably isn’t as feasible with open source projects.
For me, the biggest improvement would be the tree-view you get in Fisheye/Crucible. It's so hard to get a grasp on large refactoring PRs on GitHub.