Johnny Ringo said:

Musicals can be good if they are cheesy fun and don't take themselves too seriously - like Repo or Across the universe or indeed Dr Horrible.

Wait, are Repo and Across the Universe your examples of good musicals?

There are some much beloved musicals I don't like at all: South Pacific, Carosel, Oklahoma (to some degree), and others. Something being a 'musical' doesn't really increase or decrease my chance of liking something I guess... but I do like a fair number of musicals.

1776
Hello Dolly
Music Man
The Pirates of Penzance
The Sound of Music
Disney Cartoon Musicals
Oliver!
Moulin Rouge!
Into the Woods
Paint Your Wagon
Man of LaMancha
Les Miserables
Phantom of the Opera
Joseph and the Amazing Technicolor Dreamcoat
Mary Poppins
Chitty Chitty Bang Bang
My Fair Lady
Guys and Dolls (certain local performances)

That's all I can think of presently.

And I hate hate hate hate hate Cats.