It's a little difficult to define it for abstract music, I think. It's not a word I use a lot, but then again, I mostly listen to abstract music, and only rarely get into liturgical, lieder, or opera.
Usually for me it's a combination of depth - music that, by whatever means, rewards you for putting in closer listening, repeated listening, or any other sort of effort - while not blunting the emotional affect. I sometimes find excessively "correct" or "learned" elements (particularly fugues) to slightly diminish the emotional affect of a work, though this isn't a hard rule, and many extremely affecting works can be both highly emotional and theoretically fascinating, such as Beethoven Op. 111.
Usually for me it's a combination of depth - music that, by whatever means, rewards you for putting in closer listening, repeated listening, or any other sort of effort - while not blunting the emotional affect. I sometimes find excessively "correct" or "learned" elements (particularly fugues) to slightly diminish the emotional affect of a work, though this isn't a hard rule, and many extremely affecting works can be both highly emotional and theoretically fascinating, such as Beethoven Op. 111.