This is a wonderful book for someone just learning string theory. I'm trying to do all the problems and many of them are quite tough (I have a PhD in physics.) The thought
that these problems are assigned to undergraduates at MIT is somewhat depressing - either I'm getting senile or they are awesomely talented. Maybe a little of both.
I wish I could get a hold of the solutions (which are available to instructors). Many of the problems teach things about theoretical physics IN GENERAL which I wish I had learned
as an undergraduate (or even as a grad student.)
One of the negatives in struggling with this material is the thought that string theory is really just a step toward M-theory, which is the best candidate for a "theory of everything."
One has to master four or five different string theories and then be told that strings are really not relevant to the currently accepted theory. Since I am retired and have plenty of time, I will continue to struggle with it, but it takes plenty of patience.
In the hands of an instructor who can review (or present solutions) to the problems, this is a wonderful book.
Congratulations to Professor Zwiebach for producing a great text.