I want to give an honest review without comparing to the anime (I'll try) as every movie deserves to be rated on its own.
Let me give a summary first.
The good:
- Yamaken
- Takahata Mitsuki's singing
- some comedy scenes
- plot not dependent on knowing the story of the manga/anime

The bad:
- don't know if I'm watching hard core comedy or a musical, too bad it's a mix of both and I can't jive with it
- some awkward scenes
- female lead is a shallow character (no development)
- I'm not a musical fan and it's a musical movie so there

Cast/Acting:
I've enjoyed some jokes, Kaku Kento is a very good actor (he's funny so it makes sense the director always has him in his movies). Takahata Mitsuki is a great singer. I'm certainly going through a list of Yamaken's movies one by one, although I can see somehow that his acting is not that great (this is the 3rd show I've seen that he is the main chara).

Story/Plot:
A good thing about the movie is that the plot can standalone and doesn't depend on the viewers having read the manga/watched the anime. It's ok to watch on it's own, which IMO should at least be a standard to all live action adaptations. However, I'm not the most eager musical-fan out there, so it might be a crime but I skipped all songs (and only kind of listened to Mitsuki's solo near the end).
So if it's only the story, I think I only have one complaint. As a "nerd" I can very much relate to the characters. It's true to the title, as how being an otaku affects our daily lives. But somehow I wished the female lead is not just a hollow human being regardless of being an otaku or not. Her character could've been better. Tho I think they did well with the male lead's character development. But it's still quite disappointing, really.

Overall:
I can't like the movie. It bothers me that I don't get the movie's tone at all. Is it a comedy? Ok, fine. Is it a musical? Ok, fine. Is it a musical comedy? I definitely can't vibe with the mood since the comedic scenes really clash with the musical pieces, I didn't really watch the songs ok, but what I want to say is, the kind of comedy the movie delivers does not suit the musical quality that it also happens to have. It's like watching 3 different movies at the same time. I get it, it's not a crime to have the mood shifting, but it's just the change/flow confused me. Nothing jives. It might be the comedy scenes should've been toned down a bit to make way for it being a musical. I wouldn't mind that I guess.

Re-watch value:
It's hard to re-watch anything especially if you know there are awkward scenes/acting. And comedies usually don't do so well the second time around. Though definitely re-watch it if you wanna see more Yamaken (who wouldn't wanna see him as an otaku?).