I've never watched a drama where I didn't like any of the characters but Love Alarm managed to accomplish that.
The entire cast is full of characters that just isn't realist and there will be many times where you will ask, "Why?"
The main female protagonist, Kim Jojo, is one of the most idiotic characters I've ever met. She follows a guy down the alley just because he "has something to say." If this was the real world, she'd have been raped right then and there. She makes poor choices (when you watch it you'll understand which ones) and she never gives a clear explanation as to why she did it. The drama never explains why Jojo decides to go down this route and why she isn't fixing it. The drama plays it off and later on shows that she actually regrets it. Now, I understand why she regrets it and that she wants to undo it, but I don't understand why she isn't even trying to FIX it. She can easily explain her situation and I'm pretty sure everyone will believe her, but she doesn't even attempt it. There are so many plotholes and so many questions that the drama doesn't bother to explain or answer. Maybe because they left it all for season 2 but at the moment it's not released yet so the director cannot expect us to just accept it as it is.
One of the characters I hate more than Jojo is Sun Oh. The drama plays him off as romantic and cool, but he's actually really creepy. His character is childish and selfish and thinks the world revolves around him. Not once did he stop and think about how his best friend or anyone else around him except for the girl.
*SPOILER BELOW*
Hye Young makes it pretty clear that he like Kim Jojo. Although he never outright told Sun oh that he likes Jojo, Sun Oh already knows at this point. And you know what Sun Oh does when he finds out his best friend like this girl?
HE CHASES AFTER HER.
THIS BOI. What is going on in his head? "Hmmm. my best friend, who has always been there for me and supports me, likes this girl and she is his first crush. I should encourage him and let him have the chance to confess first because, after all, he liked her first. But, you know what, because I'm just the shelfish jerk I am, I'll go out there are whisk Jojo away and kiss her right after my best friend tells me he likes her. Brilliant!"
And you know what Hye Young does? NOTHING. FOOKING NOTHING. OMFG. And both of them made a pact and told each other to confess to Jojo at the same time. This way, it's fair to both of them.
BUT NO. N O.
FUCKING SUN OH, LIKE THE BITCH HE IS, DECIDES, "HEY, NOT ONLY DID I KISSMY BEST FRIEND'S CRUSH, I'LL ALSO CONFESS TO HER FIRST EVEN THOUGH I JUST PROMISED HIM WE'LL DO IT TOGETHER."
BITCH WHERE.
BITCH WHO.
I'M PISSED FOR HYE YOUNG.
And after Sun Oh and Jojo breaks up, Sun Oh doesn't let Hye Young go after Jojo. Like bro, it's his life. Just because you broke up with her doesn't mean he has to obey your every command.
And why does Hye Young still like Jojo? Dude, she rejected you like 10 times. Give up.
AND OMIGOD, DON'T EVEN GET ME STARTED ON FUCKING GUL MI.
SHE'S EVEN MORE SELFISH THAN SUN OH.
How is it Jojo's fault that her parents tried to kill her? Why in the world did Gul Mi come to the conclusion that it's Jojo's fault that her parents are broke? And why doesn't Jojo just fight back? Maybe it's because she doesn't want to get kicked out, but still. She should've spoken up about it.
And she thinks that everyone else is beneath her when she herself hasn't gone anywhere in life. She didn't just screw up her life and her cousin's, she also bullies a guy into committing suicide.
You would think at this point she would feel bad, but no. She continues and takes out three million won from Jojo.
And another thing, why is everyone saying Jojo is such a pretty name? No, please stop. Jojo is an anime and forever will be an anime to me.

So, in conclusion, this drama is just plain stupid and frustrating. I could barely finish an episode without getting mad at a character. I wouldn't recommend this drama unless you really like getting frustrated.