I intensely dislike almost every single one, with one exception. DH found a card for DD's birthday. The little jingle was a funny little song about the humuhumunukunukuapua (Hawaii's state fish). It was random and odd and charming. It made us all laugh.
Otherwise I find them annoying and aggravating and not musical in the least.
We had a different singing card that was also a hanging ornament. It became a family joke. It was sent by my MIL. We tossed it into the box for Christmas decorations. Every December, we unpacked the box and that card would play. We kept expecting that it would eventually die, but it never did. It was like a Hallmark version of a weird ghost of Christmas past.
Not soon enough! We have one still going strong after 3 years.
In general, I think such things are horrible but I agree with the other poster that the joy outweighs the annoyance. DS has several that he has saved and gets out once in a while.
I worked in a card store, and at the end of a season, any of the cards that had gotten a little dog-eared or were discontinued had to be ripped in half (I can't remember why) and shipped back. One of those stupid singing cards started up in the bottom of the box as we worked through the stock and played continuously throughout my entire shift. It was still going the next day when I arrived for work. My manager had dug through the box trying to find it, but it was a needle-in-a-haystack. It finally quit at some point that day, but I'll always think of that when I hear one of those cards. It. Was. Awful. but I think I'm immune now.