Developer experience has been excellent, with the obvious caveats that it has been a bit bumpy when code relocated to other packages or decomposed into individual libraries, docs have been a bit of a teething issue as well, but have largely found I that I haven't needed too much documentation as of late.
As sayem_ said, you will largely just be writing Javascript, not so much framework specific implementations, which is awesome. I've had mobile (iOS/Android) devs jump in and begin contributing straight away - that's awesome as well.
Community is the icing on the cake too. There's a really active Gitter community, but possibly to it's detriment at times. The simpler questions which would usually end up on StackOverflow are usually answered in Gitter instead, which has it's impacts (harder [read: impossible] to search, community looks small from SO perspective)
Looking forward to the future!