It's a very nice theme idea. Just right for a Tuesday. When I hit "N.B.A." I didn't really bother reading the whole clue, and didn't think the theme was very tight. Then, when I finished, I saw the unifying idea. Nice—not just some random NBA teams, but the only four that have non plural names. That gives the theme the coherence and tightness it needs. Found the clue on ALL THAT JAZZ actually a bit tough. I think the "add-ons" part threw me, as I think of the phrase meaning simply "all the related things"; the notion of adding on isn't really a part of it (though I think the clue's perfectly defensible). My only real issue with the theme is that OLD BLACK MAGIC is essentially a partial, a fact which necessitates the weird cluing, with the unexciting "That" in quotation marks at the beginning. OLD BLACK MAGIC just doesn't stand on its own very well. But overall, the theme is reasonably clever and reasonably well executed.
The fill is more troublesome. This is at least partially the result of the Highly segmented grid. Tons of black squares (40) creating tons of nooks and crannies composed mostly of 3s, 4s, and 5s, i.e. not the most exciting fill on the planet. But this puzzle's short stuff was pretty subpar, even by short stuff standards. In the same little section you have multiple icky answers: I WAS and OSE, GST and IMA, ALLA and ILIAC and OCHRES (plural) and ASTO, EERO TADA and LTYR (!). The ANDI / DVI crossing is particularly shabby. There's more, but why list it? Greater care in overall grid construction would've been nice. Also, I would've said SUBTROPICAL, not SUBTROPIC, but perhaps that's just me. Never lived anywhere where either adjective would apply.