As someone who has read the manga and watched the drama, I'd have to say the drama is far more superior. I really enjoyed watching it, and even went back to rewatch it. It was that fun to watch.

That being said, this is your typical high school Japanese drama with a twist of BL, so don*t expect it to be the next big Life on the Line (Bokura no Senjou). However, because this drama aired on TV Asahi (one of the major TV stations in Japan) and backed by Johnny's Entertainment, starring two Johnny's boys, this drama does have better production production quality than the average BL (which are usually smaller B-List films.)

STORY:

Kieta Hatsukoi is about Aoki, who has a crush on Hashimoto, the pretty girl who is seated next to him in class. When Aoki forgets his easer, Hashimoto lends him her eraser. Aoki discovers Hashimoto had written the name of her crush, Ida, on the eraser. Panicked that his crush likes someone else, he accidentally drops the eraser, only for Ida to pick it up. Seeing his own name with a heart on the eraser, Ida looks at Aoki for an answer. Aoki, being the loyal man he is, chooses not to expose Hashimoto's crush, instead telling Ida it's his own eraser. Now Ida thinks Aoki is in love with him, while Aoki is in love with Hashimoto, who is in love with Ida?

The drama is amusing, all the way from the story, to the the way Aoki acts. The story itself, isn't very original, following many of the stereotypical BL and high school rom-com tropes. However, the story is refreshing because it doesn't have any real dramatic drama. The situations the characters find themselves in are very realistic and relevant, while not being too over the top with high stakes. Any Bob, Joe, and Harry can find themselves in Aoki, Ida, Hashimoto or Aida's shoes at any given day.

If there is any drawbacks to this drama, it's that because of the lack of dramatic drama, some may find it to be too boring or unoriginal. Also, the main actors are still rookies so their acting can sometimes be stiff, but it personally didn't bother men.
I've seen worse actors before, and the actors here are decent. Not great, but decent. Lastly, the biggest thing that bothered me was that never did any of the characters kiss. There was a few hugs, but no kissing... Which I expected since it's two Johnny's boys and Johnny's Entertainment is constantly fighting against the Johnny's are gay rumors. (Johnny's Entertainment is a male only entertainment company, so all actors, singers, and talent under Johnny's are men/boys.) A kiss at the end would have been great since there was some foreshadowing leading up the the final scene. But we don't get one... Which works for Aoki and Ida, since it's in character for them, but as an audience watching, I would have liked a kiss at the end.

Aoki & Ida

Aoki is a cheerful and hardworking boy, who has wears his heard on his sleeve, while Ida is more stoic and indifferent to his surroundings, he is actually a caring young man. Once Aoki caught Ida's eye, Ida's world started expanding and he started to feel so many different emotions. To be honest, at first, Ida's indifference really annoyed me since he came off as a more mature guy, but was more naïve about love than Aoki. However, as the drama progressed Ida grew on me... But he was still so naïve, it drove me crazy. If you like Aoki, stop mulling around and just go with the flow! Aoki, on the other hand, I loved a lot. He was very cute, and his over the top reactions were adorable. He's honestly the best thing about this drama.

Hashimoto & Aida

Hashimoto and Aida were amazing supporting characters. They had a presence, with the own storyline, but never overtook the spotlight from Aoki and Ida. I really loved them from start to finish, but towards the end, their cat and mouse game really started to annoy me. I'm glad things worked out for them, but it took way to long to become happy.

DRAMA vs MANGA:

The drama covers Vol. 1-5 of the manga, and it is still ongoing as of the time I am writing.

The drama covers almost everything in the manga, and even adds extra scenes so we can get to know the characters more. However, the drama makes a few changes, like switching around the timeline of the scenes.

For example:
Drama - Aoki's tutor misunderstands him in ep. 8, while Christmas Event and Hashimoto giving Aida a cupcake is the last episode.
Manga - Christmas is not a big event. Aoki's tutor incident happens after the Christmas. Hashimoto giving Aida a cupcake was during Valentine's Day.

The drama also changed quite a few things, which I personally felt was better. Here are a few examples.

1. Kokomi
Drama - Volleyball manager(?) from another school, friends with Ida from before.
Manga - Some flashy random girl from another school that Ida befriends at a go-kon.

2. School Camp
Drama - Go hunting for food in the mountains, learn about teamwork.
Manga - Based on Skiing level, nothing about teamwork

3. Homeroom teacher
Drama - Supportive role, giving great advice.
Manga - Just around, not supportive, accuses Aoki of cheating, remembers Aoki's sister and not Aoki.

Lastly, the biggest change was Ida's personality and Aoki's disgusting reactions. In the manga, Ida thinks very annoyingly. His actions and thoughts don't match sometimes. In the drama, we can't hear his thoughts so he is only portrayed as stoic and indifferent. As for Aoki's disgusting reactions in the manga, I feel like the mangaka was trying to go for comedy, but the over exaggerated and hideous faces really threw me off. I wanted to throw the book away. Thank goodness the drama kept the reactions natural.

OVERALL:

Kieta Hastukoi is a great drama. I recommend watching it. It's your typical Japanese highschool rom-com, but it's a fun watch nontheless.