Sacrilege: I love most Sondheim, but I think the score is the worst part of Into the Woods...just too damn repetitious, and the score is the weakest part of A Funny Thing Happened, which I Love as a whole. Some clever songs, but only two memorable ones, Comedy Tonight and Everyone Oughtta Have a Maid.
I also love most Jerry Herman scores -- I even loved The Grand Tour, but I think The score is the weakest part of Hello! Dolly! I have always found myself skipping a lot of the songs when I have played it in the past. In the first place, there are not a lotta songs in it, and a number feel like filler to me or just aren't that good. Elegance, It Only Takes a Moment, Ribbons Down My Back have always been yawns to me. The only great song is the title song, although I love Sunday Clothes and So Long, Dearie.
While I don't think Lion King is a great show -- there are moments of greatness -- I think it's score is the weakest part and it would probably be a great show if it had a better score. While Dreamgirls has one of the greatest musical numbers in musical theatre history and Step Into the Bad Side is incredible, as a whole I think it's score is its weakest component.
In response to some of the other posts, I think Mame has a great score, perfect to the material...in the context of the show, I just think That's How Young I Feel is weak. I think the 1776 score is perfect for the show and is very entertaining, and periodically, stirring, just listening to the score. I don't think that Spamalot is a great musical, but I agree that the score is its weakest component. It would probably be better without half the songs, although it would be woefully short for a splashy musical. And I think that Nine has a magnificent score, which meshes so beautifully with the staging.