It's pretty terrible. ORMs like Doctrine use annotations because their philosophy is that a data mapping class should be a pure class that you decorate with annotations. I personally hate that approach and have had no issues avoiding this path over 20 years of PHP development.
Agree. The first time I ran into this, I was completely confused as to why my code wasn't running as expected. Then I noticed the strange formal structure of the comments, made changes there, and voila.
I don't understand why that feature wasn't implemented as decorators or some kind of function code. If anyone has any resources/thoughts on why this path was chosen, I would be interested in seeing them.