Hmm ... a pity that Mentar did not enjoy the movie.
I will admit that it was certainly lighthearted in it's humor and not "edgy" ... but when Hayate in general resorts to that type of humor is when I enjoy it the most.
Animation quality wise it certainly not "Children Who Hear Voices from Deep Below", but I did not think it was all that bad either - although certainly not up to "film" standards, I guess.
I agree that the soundtrack was pretty good but also admit that I am not much of a "Nagi Shipper", per se. The story is directly linked with the main series, but rather than an alternate story I would guess it would be more of a supplemental story. Must admit that I am kinda curious if it will be incorporated into the manga.
But then again I have to confess outright that I am a sucker for sappiness and fuzzy feelings (my fave series this season is Tamayura Hitotose, for example), so my opinion on the whole may not be surprising.
So yeah ... I would give the film a 7.5/10 vote overall.