Those guitar drop-ins between the vocals are way cool and presented well. The swing-time syncopation is excellent. And the vocals + bgv are killer!
I'd be tempted to push up the volume of the solo lead vocals.
The shaker/tambourine is a cool add! Is it swinging as hard as the rest of the stuff, or is it just a bit straighter?
Holy crap, there are so many awesome guitar tones in this. Great blend.
cheers,
-Tom