TL;DR: The third act ruins what was looking to be a near-perfect game.

For once, a Dragon Quest game ended on a bittersweet note. The world's been saved, but at what cost? Your hometown is a pile of rubble that now acts as a literal Last Bastion for the people that once lived there and, most importantly, a vital member of your party gave their life to save those she cared about the most.

Instead of leaving on that and letting the player roam the broken world in the post-game, looking for answers about their ancestry and the role they play in the world or testing their mettle against ancient evils that are even stronger than the second act's final boss, you discover that there has been a method to travel through time the entire game and immediately bounce to an alternate timeline before the ending events of the first act.

And with that, all the interesting character development from the second act is gone.

Without his sacrifice, Erik doesn't lose his memories.
He doesn't open up to the party about his younger sister Mia and the tragic events that unfurled prior to the events of the main game. If you decide to visit their hideaway during the third act, the Luminary just magically removes the Midas-esque curse that was placed on her and the two happily reunite.

Without the death of Veronica, Serena has no reason to ritualistically cut her hair and grow as a person, bonding with her sister's soul and unlocking an expanded skillset that makes her an essential party member when tackling any challenge the second act threw at you.

Without witnessing Jasper's betrayal and the fall of Yggdrasil, Hendrik isn't lauded as the Hero and the protector of the Last Bastion. He has no reason to have the Luminary prove himself in the defence of his hometown and pledge himself as their sworn protector once he comes to terms with his wrongdoings and the power that the Luminary holds.

Outside of the narrative qualms I had with the third act, I fucking loved DQXI. I felt like a kid again, embarking on a comfy adventure in a beautiful world with my little ragtag group of friends.

Oh and the music sucks, with little to no variety in regards to tracks and compositions that you'd expect to come from Sugiyama's understudy and not the man himself.

An easy all-time-great had the post-game/third act been different.