Here are my two cents:
I agree that having excessive information on any UI, albeit being valuable to some, may be overwhelming to the majority.
A progress bar is a good visual cue when it comes to displaying progress.
I like Elementary OS’s "less is more" approach since it is the best in terms of simplicity, although it may be a little bit too much. I see the value in offering to the user information on new features, improvements etc.
IMHO, I like Ubuntu’s approach, where there is a slideshow with a progress bar and an option to expand and see what is going on. It could probably display release notes, new features (avoiding having marketing materials).