> One thing that git stinks at is line-by-line code review, for example.

Really? That's one thing I haven't ever seen anyone do better than plain old 'git log -p'. I use this alias:

  [alias]
      review = log -p --reverse

After `git fetch`-ing I copy the hash range that I fetched and paste it after `git review`. Then in Less I can type "/^diff" to use n and p to skip back and forth between commits. I find this is much easier to read than Github's html diff views and infinitely more efficient than the millions of clicks I need in web browser to do anything (plus there's absolutely no lag, unlike the browser).