[steveklabnik]

I do not have as strong of feelings as your parent, but:

1. A lot of the APIs make use of the typestate pattern, which is nice, but also very verbose, and might turn many people off.

2. The generated API documentation for the lower level crates relies on you knowing the feel for how it generates the various APIs. It can take some time to get used to, especially if you're used to the better documentation of the broader ecosystem.

3. A bunch of the ecosystem crates assume the "I am running one program in ring0" kind of thing, and not "I have an RTOS" sort of case. See the discussion in https://github.com/rust-embedded/cortex-m/issues/233 for example.