Potentially controversial opinion: I think Google's Material Design is a bit crap.
Like, the thought underpinning it is (mostly) sound, but I find the most recent version of it just kinda aesthetically bleh and surprisingly hard to parse in my limited experience as a user.
Some bits have gotten better (the new input style = good improvement), some bits remain pretty bad (FABs = terrible UX), and I know the system is intended as a themeable baseline—my complaint is mainly with how Google themselves have implemented it.