Aaaand done. Ended up a bit over 38 hours, but I did all the quests, completed the map, and succeeded in my aim of beating the game on nightmare with no items, HP absorb effects on weapons or HP regen effects on armours. Was actually a really fun challenge doing it this way after the first bunch of bosses (excluding the first), the bosses hit HARD but once you had their patterns down they were definitely doable, they just punished you heavily for screwing up.
All in all my second favourite Ys game after Origin, Origin still has the edge because of its bosses, but Celceta was better than it in almost every other way. Really liked the cast, and Adol himself actually really shone thanks to all the dialogue choices and flashbacks - I've never been a huge fan of him as a character because of his silent protagonist status, but thanks to those two things in particular this time it was much easier to get a feel for his character and his involvement in the story. I'm sure the flashbacks were a one off but I'd really like to see dialogue choices used more in the series in future. Loved the areas, both because of their size and the variety of them, at one point I was a bit concerned most of the map was just going to be the same forest but that quickly turned out to be unfounded. The soundtrack was glorious as expected, both the arranges (with a few exceptions that were a bit mediocre) and the new tracks. Can't wait for the OST of this one. Was a little disappointed a few favourites didn't make it though, but you can't have them all.
Finished with 52% trophies, will be starting up a second run to get to work on the platinum tomorrow. Not ready to put this one down yet.