useEffect is such a weird name. I get that it's kinda general in usecases but whenever I see the name my first thought is "what the hell is an effect and when do I use them?" and this is coming from someone who has actually heard about effect systems. Going from componentDidMount which is a nice, clear name that dictates when the function is run, to useEffect(() => console.log("Mounting!"), []) is so confusing. I'm not super thrilled that the difference between running on mount, on new props and on unmount is implicitly determined via the second argument or returning a new function. I get that useEffect has a nice coherence and is more general but that's not always a good thing.

Not to mention the docs for useEffect just mention the one usecase of running on mount and on update and neglect to even talk about running something just on mount.

That being said, the reducer hook is amazing and a great replacement for overly complicated setState or overly simple Redux stores. Definitely reminds me of ReasonReact in a good way.