I remember running into this a couple years back and loving it, but I also remember stopping on chapter 300 or so. Seemed like things were falling apart, and now the ending seems almost completely nonsensical. Having read through it in full now, I almost wish that I hadn't. I was relatively satisfied with it ending after he ends up staying with Nagi after the Athena arc, but now the actual final chapter feels like it was meant to be bittersweet, but just ends up feeling bitter. It felt like it spent 500 chapters building intricate backgrounds and plotlines for every character and all of them were instantly dumped. Maria's ending is especially sad, because the author admitted that she was going to be revealed to be Hayate's sister, something that would give them both another character that they could each have platonic feelings for without it being sad, but it ended up being an essentially non-canon bit of trivia in one of the final volumes, so instead her final appearance is her getting thrown into a mob character's story.