I'm a sucker for a musical the vast majority of the time and this hit on a lot of the things I look for. It's definitely got flaws, but everyone seemed to be having a good time with their characters, Tom Cruise especially, and the performances were pretty good across the board.
The comedy seemed to to hit more than miss in my theater, which was probably about a third full. And my group of 5 people, all in our early to mid 20s left the theater very pleased with the film, and most of the others coming out seemed to feel the same way.
To me, this feels closer to 70% consensus than the near 40% it's sitting at now. Looking at reviews quickly, it looks like the major complaints are the romantic leads, the fact that it's too tame, and the fact that it's a book musical and the songs don't live up to the originals. There's nothing that can really be done about the last one, either you're open to some new performances or you're stuck on the originals. I'll be honest and say there were times that I heard the opening of a song and say I wish I were hearing the original, but most of the time they seemed to keep things fresh enough and had some fun and interesting mash-ups to give some songs a new twist.
As for how tame it is, there's no reason for this to have an R-rating and the only way to make it more wild would be to go over to R. To me, they seemed to do a good job in getting over the rock star lifestyle, and in ways it's wilder than the R-rated Rocky Horror Picture Show.
I'll give that the romantic leads were kind of weak, especially when put up against the much more charismatic veteran cast, but they did a pretty good job overall. The guy that plays Drew was definitely the weaker of the two, and they may have been better served going with play's original star Constantine Maroulis, who's already known to a good number of people because of American Idol.
I think this could end up with some decent legs and finish in the 60-80M range, as many musicals do seem to have 4-5 multipliers from their opening to the end of their runs.