1. The syntax is horrible (for writing by hand).
2. I'm more interested in computation than presentation, so something closer to S-expressions along the lines of Mathematica feels more comfortable to me.
3. The progress so far on defining semantics for content MathML has failed to impress me.
Concretely, I think if you are trying to do semantic mathematics, you need an implementation of the semantics in software, not just a hand-written spec. Ideally this would be backed by a formal theorem proving system. So far I just do randomized testing using symbolic evaluation and interval arithmetic. See this writeup for more details: https://arxiv.org/abs/2003.06181
