Agree with most here. I went in almost completely blind, and I really liked the score, characters, and even the plot but found the overall assembly lacking. It was a somewhat frustrating experience, sitting and watching whilst also imagining a better version in my head (don't know why, but I imagined a film - maybe it's just the "small" showbiz story). The problem, I think, is that there is absolutely no reason to structure the show in reverse. It works very well for Betrayal, in which we learn new information that forces us to reconsider each scene we've already watched, and in which hope and despair collide and swallow each other; but in Merrily the unabashedly upbeat ending doesn't even try to reference the beginning scenes in any way, and we don't gain any insight from seeing the final chapters first. "Not a Day Goes By," for instance, is more moving the second time around because we're familiar with the character, despite the fact that the original song is the longer, more dramatic showstopper. I think this show would be a very compelling slice of life piece if reordered chronologically, save for the final scene on the rooftop, which should stay last - a flashback while Frank despairs over his empty Hollywood life - followed by perhaps an added coda with Frank and Mary.
The production is very well sung and orchestrated, but that's about it. Aaron Lazar's got a tough role - the Marcello Mastroianni type who seems absolutely empty but is secretly filled with dreams, longing, etc. He's a strong singer but a bland actor. Wayne Brady is miscast. Donna Vivino is the best singer of the bunch but her acting in the first scene is quite bad and I was surprised at how little Mary actually had to do other than pine after Frank. Saycon Sengbloh is very brassy and very very hammy; I would've liked to have seen a quieter and more subtly seductive version of the character.
But that's really my complaint with the whole cast. Everyone's doing their best "look ma, I'm in a MUSICAL!" mugging when really this appears to be an intimate, naturalistic play with a nuanced Sondheim score woven in.
As for Arden's direction, it was very ho hum. The dressing room set didn't really add or detract, and the "ghosting" that's been frequently mentioned is hardly noticeable except at the end of each act. I agree with the poster who said he felt like he needed a concept but didn't really follow through, or, for that matter, come up with an original one.