1. Smoother sound, a little more texture
2. Better separation of instruments. Oddly closer to tube in a way
3. New layering is present I do not recall hearing prior
4. More to the bottom end it seems, not imagining this
5. Weighs less now, easier to lift - just kidding, lol.
@decooney It seems the above, which seems important to you, is your answer. But that doesn't come from the class of operation so much as whether the amp is competent. As an example there are class D amps out there now that easily challenge the best of what class A has to offer.