I started this manga when I was 16, and now I'm 27, and just finished it yesterday...at first I had mixed feelings. I like the build-up and they actually made me care about the whole Royal Palace thing despite being way more interested in how the characters end up.
I think the one weird thing for me was how Hina's confession was cut off, I expected us to get back to that at some point but we just...never did. At first it was hard to accept Nagi being the one who won, simply because it seemed like it was leading up to the girls dropping one by one and it naturally seemed she was one of them.
But after thinking more about it, even if there's some argument for the ending being rather open since it could just be Hayate wanting to be back in Nagi's life to help her, now that she has matured and grown, and they can stand as equals, the more I realize this ending is fine. Hayate admited initially it was a misunderstanding, and when he was asked if he loved Nagi he had no response. It's not impossible that he hadn't even thought about her that way since he was so focused on being a butler. When given some time, he decided he did want to continue being with her.
Which would mean that when Hina confessed, he couldn't accept her feelings because he was still processing his own.
Through all of its flaws, this is a series I will always hold dear, that has made me laugh so so much and tear up, and feel all sorts of emotions, and it all started with a misunderstanding.