I still don't have an answer

This whole workshopping thing, has brought to mind a question that I have grappled with in the past and still have no answer to: How do you tell a friend that you don't like their creative work?

I find that it is much easier to convey what I'm saying is if I have something constructive to add to it.

I'm not into __ because of __, but if you're going for __, I like __ part works well, and __ part is a little too __.

Unfortunately, there have been times when my honest opinion is, "This piece, that you have put so much heart and energy into, is terrible."

Phrase it as a question? "Is this piece, that you have put so much heart and energy into, supposed to suck?"

Example:

My friend recently started a new band and the first song that they released was not to my liking, and I just had no way of telling him. It wasn't the entire song, just about the last two thirds of it, but I had no explanation or any helpful way of phrasing it.