This film has some excellent parts, but I'd recommend giving it a miss. The anime's much better, as is almost certainly the original manga (although I haven't read that).
It's a love story between two otaku. Mitsuki Takahata plays Narumi, a manic loon who got dumped by her last boyfriend for being an otaku and so is now under the impression that she's hiding it. Ahahahaha. Kento Yamazaki plays Hirotaka, a deadpan gamer who doesn't seem to care about much. They're childhood friends, but now they're working at the same company.
Hirotaka becomes Narumi's boyfriend almost immediately. He bribes her by offering to help her sell her Boys' Love doujinshi at Comiket. The rest of the film is their eccentric relationship progress.
The film's biggest strength is Takahata. She's a firestorm of energy, her reactions made me laugh and she's putting in everything she has. She's playful and flexible. It's almost worth watching the film just for her, if you can swallow everything else. (The film's not dreadful. It's not Nisekoi, although it's on that spectrum.)
The film's weaknesses are two: (a) the tone, and (b) Yamazaki.
Firstly, the tone. It's not piss-off-and-die silly and we're only talking about a bit of mild pollution rather than nuclear waste, but it's afraid to trust its script and actors. It thinks "comedy manga" means "I have to be silly". Someone blinking might have cartoon blinky sounds. Jirou Satou's performance seemed bold in his first scene, but later became absurd and annoying. The cast regularly burst into song and dance numbers, which are never good and tended to make me hit the fast-forward button. (No, I tell a lie. There's a stage show by Uchida Maaya, at which one of her songs is her theme song to Gonna be the Twin-Tail!!, which I've always liked. Alas, the film doesn't let her finish it.)
The film's basically okay. I liked its portrayals of Comiket, for instance, which had more reality. Takahata can pull off anything. But there's no chance of me rewatching it, whereas the anime is lovely.
Then there's Yamazaki. I've liked him in some things without particularly rating him as an actor (e.g. One Week Friends) and actively disliked him in others (e.g. Death Note), but this performance is in the latter category. He's not doing enough. Yes, that's the role he's playing, but even so. It's possible to do more than this even while ostensibly not reacting to anything. If you rewatch, for instance, the scene where he's just absurdly transformed himself into an anime otaku, it's possible to follow the actor's processes and intentions... but they're completely unsuccessful, since his expression of them is external and dead-eyed. I don't believe that the character he's created would have behaved like that. I get nothing from his interactions with Takahata. No insight into his emotions, insecurities, desires or anything else. He's a human robot. His manner suggests absolute confidence. He's pretty, sure, but that won't stir half the audience.
There's a good film buried in here. You could make an explosively entertaining fan edit by cutting about 40 minutes of material, starting with all the songs and as much as possible of Yamazaki's screen time. There are some interesting questions in here, as the film grapples with the otaku experience and the issue of whether or not one should hide one's true self. Takahata I could watch all day. She's funny. Her, I'd recommend watching.