OK, so I saw this Saturday night.
I will front load these comments by saying that I have been a huge Gloria fan since I was young, even longer than I have been a theatre nut. So I've been looking forward to this ever since I heard that two of my favorite passions were mixing.
I had a great time. My 12 year-old Gloria fan loved it. My more mature developed taste in theatre had to be checked at the door to be honest. But I do think everyone should see it. Because Gloria's story is awesome and that music is killer.
It's not the worst jukebox musical...in fact it is probably in the top 3 of all the jukebox musicals I've seen. But I don't usually like jukebox musicals. As a comparison, I thought Beautiful had some admirable qualities, but overall, was pretty craptacular (especially that book). I like this book a little better. Basically because they found some genuine humor in some places.
Some songs were clearly being stretched to work where they wanted them to fit (for example a beautiful and lesser-known song from early in MSM's career called "When Someone Comes Into Your Life" is given to the spirit of her father to sing to her, but is clearly a song written for a dumped lover to sing...so a little awkward...but such a beautiful song that everyone should hear!)
Some songs were used well ("I See Your Smile" and "Reach" were appropriate and moving inclusions I thought) and one even transcended itself ("Wrapped"-which I will never be able to hear the same way). And I totally forgot about that "Famous" song so kudos for pulling that out of the vaults. The new song written for the show was nice...
Here's the thing though, Gloria's catalogue has some really great songs that have inherent conflict and storytelling in them, but they weren't used ("Words Get in the Way," "Cuts Both Ways," "Always Tomorrow," "Nayib's Song," "Close My Eyes," "Your Picture," "Mas Alla"
so it did seem a bit low on the conflict. And then they kind of took out the awesome story progression from "Here We Are" and turned it into a generic love song...which it isn't.
BUT, positives outweigh negatives I thought as far as music was concerned.
I've never loved Sergio Trujillo's choreography and this show unfortunately did not change my mind. I just wanted more. I feel like some other choreographers could have choreographed the **** out of this and made it a little more the dance spectacle it should have been.
Technical elements were nothing to write home about, but still the show added up to greater than the sum of its parts.
Loved Josh Segarra. Found humor and pathos in many moments. Great work. Thought Ana Villafane was pretty good. Genuinely sounded like Gloria speaking many times. Andrea Burns was super-solid as always (although she seemed to be struggling a bit vocally towards the end of "Mi Tierra"
and Alma Cuervo was an absolute delight.
Audience seemed to love it. As did I. Even if it doesn't seem that way. 
If the creative time is looking for things to change before opening, I'd say play to the strengths of that music and amp up the dancing element. The "Wrapped" dream/surgery sequence is almost really stellar. Needs one other cool scenic element or staging trick to make it remarkable. The record exec in act one is a bit over the top mustache-twirley. I didn't buy it. Just tone him down a bit so he seems less cartooney, and I might not roll my eyes as much in that section (loved Emilio's speech to him about Americans though...nice touch).
Oh, and two things that would have been nice, but its probably too late for now:
Would have been cool to have found some way to have a giant jungle-themed Rhythm Is Gonna Get You production number that wasn't part of a medley.
Would have been cool to explore some of Gloria's activism and such after the accident. To me, that is one of the major things that makes Gloria unique as a pop artist ... and is even cooler than Emilio's determination to make her a star (which I feel like this show focused mostly on). You know, this book almost showed us more of what was unique about him than it did her.
Any way, go see it! You'll probably really like it. Especially if you check your theatre critic at the door and just give in to the joy and goodwill of their story. Then go take your inner theatre critic to Hamilton and Spring Awakening and you'll be fine 