Rhapsody in Blue is a prime example of instrumental/classical that holds attention and is both beautiful and interesting. A lot of what traditional classical lacks is that sort of energy and excitement brought about by rapid changes.

Another thing it lacks a lot is unity with that variation. For instance, Rhapsody in Blue has a specific recurring tune that resurfaces from time to time to hold the piece together. A lot of the classical music I hear shows way too much degression, and fails to balance variation and unity.