I enjoyed FFXV's gameplay, but I agree that it could have evolved a bit more. Though my opinion isn't solid since I haven't played the Royal Edition, which contains an upgrade to Noctis' Armiger mode. People that have played the evolved form of Armiger said it's the additional layer of upgrade that the game was missing.
Square incurred in losses after the expenses made through the opening of a new studio based on the Luminous Engine, reason as to why every DLC except Ardyn's got axed. And I'm pretty sure Ardyn's wasn't canned because they were pretty much far in its development, plus the anime special.
Well, if you want more from Gladio, Prompto and Ignis, it isn't bad. But honestly, Gladio's isn't very good, but they get better after every subsequent release (Prompto > Ignis > Ardyn).
Ardyn's was the only piece I payed for, and double price, seeing as how they had doubled the price from the last three we got.