I think the Harry Potter movies are awful
Why did you watch them all, then?
I heard that the movies are quite popular
It is okay if you do not like them. They are not for everyone, it is okay if you have different movie tastes.
But I heard that the books are great!
Personally, I think that the books were indeed great, and that the movies were a bit less so.  It's perfectly fine to disagree with the masses regarding pop culture, but if you haven't already, maybe you should try reading the novels.  If you don't like them, then you can just stop reading.