So far, we've seen only two different genres of vocal music featured in the show:
1. Musical numbers (Find a Pet, The Flim Flam Brothers)
2. Pop (more or less the rest of it)
Personally, I am not too fond of either genre in general, but I'll listen if it's tied to another good piece of media and not just standing by itself. Pop music and musical numbers are the most technically shallow genres of music, and people often listen to them not just because they necessarily sound good - they offer some sentimental value or are being played in conjunction with something else (like a music video, play, etc.)
For example, if I listened to Rarity's "Becoming Popular" by itself without having being acquainted with the show, I would have gagged and muted it. But, since I am a fan of the show, and Rarity is my second most favorite pony, I am ready to loop it for hours on end under certain conditions.
I would love to see a jazz score in the future, if it is within Mr. Ingram's capability to score one. MLP: FiM needs to move beyond Broadway inspired musical numbers and bubblegum pop.