My sister LOVES Mills and Boon, I've tried one but I couldn't even finish it, as Janet said, they're very predictable (and cliched). As far as I can tell the men are always arrogant, the woman are always ridiculously vulnerable and there's always a happy ending.
Saying that, I never go for any type of romance book, they're just not my thing, so maybe if you like other romance you might like Mills and Boon?