- sub commands (and sub sub commands) provide a high level abstraction over the many different tools and features. The "toolkit" approach allows for easy expansion and refactoring of individual features, and is entirely pluggable by end users. It even provides tools to interface seamlessly (git rev-parse --parseopt; rev-parse is amazing and allows you to wrangle git types trivially). Git also doesn't care what language you use. It ships git subcommands in C, shell and perl, but you can use node, python, bash, go, whatever you like. Really great.
- git divides it's interface and features into porcelain (user facing) and plumbing (internal; used by porcelain implementations). This allows them to avoid breaking changes while providing new and exciting features. This is a great design choice and it's been copied extensively by many projects, but I've never seen it pulled off as well as git.
- git consistently reuses terms and objects (there have been some missteps over the years but the maintainers are very humble). Commit objects, refs, dates and times all work the same almost everywhere.
- git is extremely well documented, both in its man pages, online and within the tool itself. Help flags and interactive messages and descriptions and suggestions of what to do next. Have you ever performed an interactive rebase? Or resolved a merge commit? Or corrected a tracking branch? Just great stuff.
I know we love to hate on git here but let's just for a moment acknowledge this wonderful, powerful tool for something it does a great job at. Git cuts no corners, it's consistent and trustworthy, and a hallmark of modern day software engineering and UX.