This soundtrack is absolutely massive. I think it's great that so many tracks made it in, even those that aren't KSA originals. I'm sure that some would say that it's a bit bloated, but getting so many great Kirby tracks in such high quality is totally worth it.
The originals definitely have their own style compared to the other modern Kirby games, and while it's not as distinct as Planet Robobot (obviously), the increased variety of instruments gives so many songs their own unique flair. It's a shame that there seems to be no main connecting theme like Sun, Sky, Dreamstalk or The Noble Haltmann, but that just opened up the door for remixes of more obscure Kirby songs like the Casting theme from KDL3, Yearning for Yellow (Vroom!), and even the theme of Kirby GCN. The highlights of the remixes are clearly Morpho Knight's themes and the Celebration Picture themes.
The original themes in general seem to be good at worst and amazing at best, although the stage themes often fail to be very memorable. It's clear that some of the OST's bests are original themes that include some elements of older themes, like the theme of Heroes in Another Dimension and Astral Birth Void's theme.
Returning themes are again, great, but they have introduced me to some other amazing Kirby OSTs, like Blowout Blast's shockingly amazing OST.
The whole package is great in every way, although some themes may need to have their titles corrected and edited.