I saw it and the premise is very, very clever. Yes, the Philly actors were excellent, particularly the actress who plays Linda Eder's rival, Rosalind. Whoever ultimately gets cast in that role is going to walk away with the show, regardless of how great Linda sings.
Linda's role of Irene Fontaine needs BIG-TIME development. Between songs, she's just not a particularly interesting character. There isn't enough backstory on her character, unlike Rosalind, whose whole backstory is one of the main comedic themes of the show. Irene is defined only by her reactions to the other characters and Linda's lines end up to be stuff like, "You idiot!" and "How could you do a thing like that to me!"
Her songs are good and she sings the bejeesus out of them as only Linda can, but the authors are expecting the songs to do all the heavy lifting where character development is concerned and it doesn't work.
I see good things ahead for this show because it's got so much going for it. Very inventive with concurrent plot lines that get tangled together in a really fun way. The second act sounds like it's great. Linda looked great, was in terrific voice and seemed like she was having a lot of fun watching the other actors, but she needs a real role to play here and right now there isn't much for her to work with.
Criticism is prejudice made plausible. -- H.L. Mencken