Yes, you are right, the speed is great and the concept is actually quite interesting. What annoys me is the fact that they broke the UX on iOS (don't know about other platforms);
- you cannot scroll to the top by typing on the bar at the top on the screen
- there's this AMP title bar at the top, that's super annoying. I read, they might eventually add the option to hide it
- feels like they tried to implement smooth scrolling what conflicts with native iOS smooth scrolling resulting in not-so-smooth scrolling
Finally, and that is more important I'd say, we have the whole point about the openness of the Internet. People are concerned about what Google (and Facebook) does because there is the potential to create a walled garden of exclusive content not everyone can access - which would actually contradict the idea of AMP, wouldn't it?