There's a HUGE difference. A book reviewer reads a book, then writes something about it for a newspaper or magazine (or a TV or radio presentation) that will tell, very briefly, what the book is generally about, without giving away too much, and either praise the book or pan the book. Or dismiss it as 'just another book'
A critic, on the other hand, is going to put the book under a microscope and examine it from every angle. The critic is going to point out any weaknesses in the structure of the book, in the characterizations, in the action, and certainly will point out any flaws in the book itself - anachronisms, for one thing, or geographical misplacements, or political misalignments.
A reviewer might be likened to your best friend, who reviews your paper and tells you that it's pretty good.
A critic might be likened to your teacher, who is going to take out a big red pencil and circle every single mistake in the paper.