Let's see: For the first 45 minutes of Jelly's Last Jam, I had no idea what was going on because no one onstage articulated. It took Phyllica Rashad's entrance to bring the show to life, and by that point I didn't care. I did sit through the whole thing, though.
Rent: I thought it was loud and obnoxious and I didn't care about the people, whose problems would all be solved if they just got a job. I stayed through that whole thing too, though.
Parade: What a ghastly idea for a musical! Furthermore, the young lady on whose murder the show turns, is dead and gone ten minutes into the show, and the rest of the show focuses on the trial. We never understand who Mary Phagen was and why she may have died, nor are the Franks likeable people, so we don't care about them.
There's a really uncharacteristic song at the end of the first act where Leo sings about seducing young girls which is all wrong. I left at the interval.
King of Hearts. This I left at intermission as well. The film is so enchanting and magical, but the musical puts the themes in a different light and takes away all the charm that made the film work so well.
Timbuktu: Eartha Kitt couldn't save this dreary, dreck-filled variation on Kismet.
I'm sure there are one or two more over the years, but right now, I don't remember what they are.
NYC Visitor and Broadway Fan