The changes feel extremely conservative. That's ok, but it's not exactly "exciting" nor is it scary.
That is my impression. There are some changes, but I can see how this could have been a 1.10.0 release as well.
Git's release numbering scheme (if there is any 'system' to it) is mysterious to me.
I think they increased the major version number because they did break backwards compatibility for a few things – the biggest of which is the default `git push` behavior. Relatively small breakages, but this upgrade is probably the only time they are allowing such changes.
Yes, Git is maintained very conservative and a lot of effort is put into review and testing even before patches hit the 'pu' or 'next' branch (Git's staging branches), where they usually cook for some time before getting merged (if at all).
I even use pu on my work machine to be able to test and use the latest features and never had a serious problem.