She is average, with bushy hair and big teeth.
In the first book she is introduced as:
"She had... lots of bushy brown hair, and rather large front teeth."
In the 4th book she is described as:
"Then two girls appeared in the kitchen doorway behind Mrs. Weasley. One, with very bushy brown hair and rather large front teeth, was Harry's and Ron's friend, Hermoine Granger."
So basically the same throughout those 4 books.
In book 4, it is made clear on many occasions that she has exceptionally big front teeth which detract from her appearance.
From Hermoine's original description it can be said that she looks average, but with bushy hair and big teeth that detract from her appearance.
With her teeth shrunk, and hair tamed- she looks stunning.
As we can see Hermoine is much more attractive without her big teeth and bushy hair.
In general her appearance is improved by her teeth having been shrunk to a normal size.
From reading the book I would say Hermoine is average looking. In general JK Rowling never describes her appearance beyond the hair and teeth, except on the special instance of the Yule Ball. Hermoine is not distinguished by her looks, but by her intelligent, wit, and wisdom, and also by her ethical stand and steadfast loyalty.