Web animation competitor review

I've been asked to do a competitor review and one of the things I should focus on is use of animations. It makes sense, since it's so popular nowadays. Problem is I can't pinpoint which parameters I should use.

I read some articles online, including Material Design, and picked the following:

• Doesn't compromise usability
• Guides users
• Follows the laws of physics

Gave a grade of -1 to 1 to each site we liked. However, most of them broke the rules. This discrepancy made me wonder what makes a good web animation? Are we still in experimental phase where there are no rules? Is that what makes an interesting web animation? What about usability?

I don't want to start a debate or write a dissertation on my report, I just want some basic parameters so we can have a direction in case there are few resources.