This really doesn't look much different from V3. The main difference is, I suppose, that it transmits your private data privately. That's good, but why it's taken until V4 is a question worth asking! What's worse is that many booksellers and libraries use ADE to transmit ebooks to their customers and in my experience with V4 so far, V4 is very unstable. In fact, I've had to follow the recommendation of one bookseller and go back to V3, which the seller said "is more stable." Basically, V4 was not able to download certain ebooks properly and as a result the entire application would crash if those ebooks were opened. It actually downloaded the full file but because, according to the seller, the metadata from the publisher was not complete, ADE crashed. At any rate, I really don't like ADE as a general ebook reader. It's too chatty. I pay for my ebooks so I don't see why my reading habits or whatever need to be collected.
The problem is that there really isn't a good ebook reader for mac as far as I know.