Why I say that? Because the source material is not great. It suffers from lack of direction, lack of character developement (too slow for the lenght of the manga) and plotholes. I never understood why it was popular at the time and it's one of the most boring and plain shoujo mangas I've ever read (and shoujo is pretty much what I've ever read).

One of the biggest problems with this show is that the source material is a romcom/slice of life manga, here though, they have decided to cross the line to drama and even some melodramatic moments becoming something of a terrible mix to me.
Why is this show called Good Morning Call is something I'm still asking myself after finishing it. They took the names and the very general idea but it doesn't follow the manga much and the characters are generally not like the manga either.
Both the protagonists are like the manga ones on steroids, especially Nao. In the manga she's your stereotypical teenager (also to point out they're younger in the manga when in starts than in this show), she likes shopping and looks... and something quite outdated it's precisely the whole girlie obsessions with the looks, weight and fashion. I'm sorry for Haruka Fukuhara, I don't know if she was forced to do it or it was all her, but she was way too over the top, exaggerated and very annoying most of the time. While Nao in the manga can be annoying at times as well, it's 100 times more in the show. Same happens with Uehara, sorry to the actor as well because I don't know if it's just his limitations in acting or the direction, but he had pretty much one single emotion the entire time. Manga Uehara can be cold, serious, sarcastic and rude sometimes but in most cases corrects himself later and he does show more emotions and he can laugh and be sassy. Show Uehara is just a rock, it was ok in the beginning but it got ridiculous pretty quickly.
There are many instances in the show where a situation happens that actually happened in the manga as well, but where in the manga was either slightly different or Uehara reacted in an ok way, in the show they cut before that or they changed the details what ended up making Uehara a lot worse of a person than he is in the manga. One example of this is that night when Nao goes to buy pudding and there was in the news something about some instances of attacks in the area. In the show she watches those news, has a fight with Uehara about the pudding, he shouts at her to buy replacement and later when she's scared he finds her in the bushes. You think, WOW Uehara is terrible! In the manga they fight for the pudding and Nao pissed saying he's like a child goes to buy a replacement pudding. Uehara sees on tv the news of the attacks and he runs down the stairs and catches here as she exits the elevator, uses the excuse of buying milk to accompany her all the way, and they banter and fight-play about who had to carry the bags back home. There are many times in the show that they made noticeable differences that make Uehara look so much worse than he's supposed to be.

I think had it followed the manga it would have been better, here they also decided that every single male had to fancy Nao and every single woman had to fancy Uehara, I would have preferred it to be less focused on the leads and they had explored the side characters more as well. Abe Jun is a very prominent character in the manga and they just put it in the background.
I also noticed there were contradictions in some of the things said in the show, for example, we see Kitaura mostly only talking and interacting with Uehara but at some point later she says to him she has to position herself (on some issue happening) with Nao because it's her friend....hmmmm excuse me? In the show you see them interacting like maybe once. It's not the only time this happens, and it felt like they wanted to link more to the manga but they couldn't remember what they had written before. In the manga Kitaura (and her cousin that doesn't appear here) were friends with Nao first and didn't have as much interaction with Uehara.

Daichi, who are you? Who knows, just created to be one of the interested parties and I learnt nothing about him other than he likes Nao, not even in the second season.
Itchan was cool in the manga, here it's just reduced once again to be another potential lover for Nao. Something that annoyed me the most about his character was that melodrama about wanting to quit the ramen shop, in the manga ramen is everything to him to the point he actually starts dating a girl he met in a queue to a famous ramen restaurant because she also loved ramen, what I thought it was funny. Also, his father is so much more stern here, in the source material he's kind and has health issues what it's also the reason his son works in the restaurant. Moreover, when the bowls were broken in the show the father is scolding Itchan, in the manga the father sends Itchan and Nao to apologise to the owner and the bowls turn out to be not that expensive per se but the old man says they were made by the woman he fancies so they're priceless to him. The woman he fancies turns out to be Nao and Uehara's landlady, and they start dating and even both accompany the young group on a trip, I thought it was hilarious, and had they sticked to a romcom with this show it could have been so much better. Also Uehara has such a cool relationship with the landlady, almost like a mother figure to him.

I could go on and on but it's no point. Generally the frustration is that if you're not going to follow the source material at least make it better, not worse... Here characters are bad and not explored, plot is thin, love triangles are boring and bring nothing to the plot, music is annoying and the over the top acting of the main character is the cherry on top to make this whole show difficult to watch an enjoy, so I can't recommend.