I have read the first book. Checked it out of a library one day when I was curious. And, like Estamos, I found it to be rather darker than the sanitized Disney version (naturally). Salten, like his Teutonic predecessors Jacob and Wilhelm Grimm (the famous "Brothers Grimm"), tended towards, well, GRIM material. Not that there aren't lighter and happier moments. But anyone who hasn't yet read the Salten books may be in for a bit of a surprise.
Kind of the same reaction I had to J.M. Barrie's original Peter Pan
story. (Yes, I know Barrie was English.) Rather a bit darker and more pointed than the once-again sanitized Disney version. The story tells more of the double-edged sword that youth presents...and that wanting to stay young forever can be (as Peter Pan does). The Columbia-Tristar live-action version from 2003 (http://www.imdb.com/title/tt0316396
) treated the book more faithfully than the Disney version. And perhaps, one day, Hollywood will do the same with Felix Salten's story. Though I don't know whether or not they could pull it off in live-action. Maybe hardcore CGI, but I guess time may tell.
Not that I disliked Salten's book, mind you. I just found it to be darker than the Disney cartoon. And having read it as an adult, after having remembered seeing Bambi as a young boy (and having loved it), it was a bit of an unexpected twist.