It's fine, just for information, the words "share" or "give" or "offer" would be used more in this sentence than "tell". "I'd like to start off by offering my opinion of the book."

Yes :) Is this for English class? Did you write an essay about a book?

Hi, Luca, Anybody would be able to understand what you mean; it's perfectly good English. If you're writing something formal, though, I'd say "I'd like to begin by giving you my opinion of the book." (I'm an American, though; this might be different for other English speakers).