The one good feature of HTML 5 was the introduction of boolean attributes. It's a feature XML could and should adopt.

The whole handling of custom elements was fumbled beyond belief. The HTML spec is a disaster particularly it's parsing rules the complexity of which is used as excuse by HTML spec authors not to improve the language.

XHTML was a better path.

I think the reason we don't see too many people complaining about HTML 5 is because not many web programmers use it directly, most are using JSX.