dont know about the android versions but i just played with iOS version and it is weird. I dont really like Apple’s apps too much but iBooks far superior to any other book app i’ve ever used. with the google play books. you can’t open-in epubs directly in mobile, you have to use the website. the interface is so archaic and weird compared to the new gmail or google+ apps. But I know it’s not a high priority area for Google so I can understand.
I do appreciate the ability to side-load books at all though.