I use Google books often, and found the lack of ability to preview books in full screen annoying enough to write a script about it. It will perhaps be useful to other people too, so I have uploaded it here. You will need to install Greasemonkey. Greasemonkey is also available for Chrome, but I have not tested my script on Chrome (although there is no reason it should not work).
Click image for a screenshot-
Feedback and bug reports invited.
Update: I have found a trick that works even better with some books. Add “&output=reader” in the address bar right after the id of the book and you will be taken to the Google play preview of the book and you get an ebook-reader kind of experience. This only works for books that have been added to Google play though.