I half disagree with the third point - the documentation is certainly lacking (I recently used Redis on an HHVM site, and the adaptor had no documentation that it even existed; just read the source to figure it out), but it's a new-ish, fast-moving project, so that's not too surprising.
The code quality, however, isn't 'bad' by any stretch of the imagination. The FB team managing it is very knowledgeable about PHP internals, and are appropriately strict about determining what zend-compatibility fixes to commit. Their code's overall quite well-written, which makes me care a whole lot less about how poorly it's documented.
Odd. If I recall correctly, there was even a detailed FB PHP coding style guide in the HHVM Git repo; that was afterwards removed though - I don't know why.
The code quality, however, isn't 'bad' by any stretch of the imagination. The FB team managing it is very knowledgeable about PHP internals, and are appropriately strict about determining what zend-compatibility fixes to commit. Their code's overall quite well-written, which makes me care a whole lot less about how poorly it's documented.