My problems with React:
- They try to push a programming paradigm, without considering that other programmers may have different or even better paradigms.
- They put too much functionality into a single framework.
- Frameworks are a bad idea anyway. It is much better to divide functionality into self-contained libraries.
- They try to redo what the web, a huge standardization effort, is doing.
- React does not fully support all HTML/CSS constructs.
Now all of this isn't really a problem right now. But if React grows and gains more traction, then it could become a problem (just like Internet Explorer became a problem after a while).