I just downloaded it and am still "kicking the tires", but so far it seems "clunky" and hard to navigate since it obviously uses the Safari browser instead of being a stand alone app. I can just go to books.google.com on any browser and not have to work within their so-called app at all.
Also, I downloaded a free book on my iPad and then downloaded another free book on my computer using the same account and as the old saying goes, "...and never the twain shall meet!" Unless I am missing something, what shows up on my iPad does not show up on my computer and vice versa. At least with the Kindle system, once I buy something through Amazon, it is available on all registered devices.
(EDIT: My bad. I was on 2 different Google accounts which is why they weren't "in sync".)
Although the Kindle app itself is only an adequate reader, the overall "Kindle experience" of content selection plus being able to sync books across multiple platforms still makes it the overall winner in my book! (no pun intended)
EDIT: So far, there is nothing about the Google eBook system that makes me want to change my buying and reading habits.