Another problem with Merrily, the show itself, that I didn't mention but should have - the show's best song, Not a Day Goes By, is sung in act one by a character we've never seen before and who's been mentioned in passing about twice. That's the structure not working, because at that point we know nothing about her and yet out she comes and delivers a really emotional song (that this actress chose or was directed to belt the entire time - a choice surely, but four minutes of anger at one level from a character we've never seen before, doesn't work, at least not for me it doesn't), a song she hasn't earned. Later, there's a reprise of it when the characters are younger and we know her a bit better, but I'm not sure how you make that first version work better.
