So much of the music has stuck in my mind like glue. The soundtracks for the four main games have gotten progressively better imo. Love how the final boss theme is another remix of the "main theme" for the game (Time Gear in PMD2, Theme of Hope for GTI and the Partner's Theme here), and the Tree of Life: Roots theme has really, really, really grown on me, no pun intended. (Also, is it just me or does it include a remix of the Magnagate theme from GTI??)
When I played my first side-story dungeon in Chapter like 4 or 5 and heard Ragged Mountain's theme, I legit stopped what I was doing and stared at my 3DS screen with my mouth wide open in a smile. The amount of recycled tracks from GTI does feel a bit like overkill at times though, especially postgame (however, I've only gone a very shallow length into postgame so here's hoping). Lush Forest set the tone for the soundtrack very early on, and I love how there are three different variations of the general boss theme from Red/Blue Rescue Team that's existed for roughly a decade now - it was a great touch (especially the rock variation which I didn't expect). I also grew attached to the School Forest theme. Revelation Mountain was truly awesome (I'm guessing the producers loved it too, because they made you listen to it twice in the plot and not once haha) and gave me shivers. Gentle Slope Cave sounded like a spy mission, which was unique and I liked it.
Every theme used in stone limbo was incredible. Abyssal Badlands set the tone beautifully....the most eerie piece of Pokémon music I've heard thus far, minus maybe the Eterna Forest ghost house theme. Reverse Mountain was majestic, Prehistoric Ruins was grand, Road to Primeval Forest was captivating, and Tree of Life: Roots is arguably better than Temporal Tower, certainly on par with both Temporal Tower and Sky Tower, and heaps better than Great Spire. Although personally, the Tree of Life: Trunk theme was a bit of a momentum killer and wholly unnecessarily subdued the mood of all of the events taking place.
Both final boss themes were far better than their GTI counterparts, the first theme especially. Although the voices at the start of the second theme instantly gave me chills. They don't quite fit the presentation of the final boss better than the Bittercold's themes, though. Also, I love the amount of old and new boss themes overall - kinda wished that there was more variety still, like with Palkia as mentioned, but hey, I'm not gonna complain about so many boss themes included in the game already.
Overall, I think the soundtrack is the best in the series, so far. It has the sound and song styles of Gates' with the punch and catchiness of Explorers' and includes so many themes from those games as well. Also, thank god there's a jukebox. That's another thing they got right.
That and Fire Island Volcano. I have listened to that theme for 6 hours straight without getting tired of it. Whoever wrote that, I want to buy you a cake.