Days is among one of the best sports manga that have been published and I'll do my best to explain why. I am not a big football fan but I do know the game and I really enjoy related manga. Area no Kishi and Ao Ashi are also great reads.
This manga finished end of January. I read it mostly in Japanese since English chapters are slow to come. Intermediate level is enough to understand all dialogues.
The story starts without anything spectacular with the protagonist Tsukamoto Tsukushi, weak nice guy, no skills, nothing outstanding. In contrast, deuteragonist Kazama Jin (gotta have something to do with the author being a fan of the Iron Fist Tournament I presume) is a genius, good looking and talented at everything he does. The story starts nicely by introducing them and how they got to be great friends at Seiseki (their high school) and how a ghost like Tsukamoto started to change day by day, thanks to his friends and his "addiction" to football.
Now the art is rather good, mostly on the realistic side but sometimes it's not up to par. It seems more cartoonish in the beginning but then gets more detailed and despite the myriads of characters popping up, it is still possible to distinguish them without giving strange hair colour. And this is great in my book.
As for the characters, that's the soul of this manga. We have Tsukamoto the weak guy with a power boost cause it's a shonen manga but his evolution is nothing crazy like his father's genetics allow him to have superpowers on the field. No, the guy is definitely hardworking, faces many hurdles, becomes disheartened and then gets back up again cause that's how you move forward. Going the distance. Kazama on the other hand is a genius and have less issues on the skills side. But nobody's perfect. Like family. Then we have Mizuki, the good looking Seiseki football team captain. The guy is an idiot, can't speak for himself and only started playing football in high school as a sub. Turns out he's a beast, genetically gifted, a powerhouse on the field and already recruited by Kashima Antlers to join them after graduation. But that's not all, there are many beasts in Seiseki: Usui a center back genius who's the vice captain, Kimishita a midfielder with supreme accuracy for freekicks or even Inohara the fearless goalkeeper. But that's only for Seiseki. Then you have other schools, Saku High which is kind of a nemesis to Seiseki, Ryouzan, Seikan... and they all have at least one beast in their team, national level pro football beast. Can't have it too easy for Seiseki.
So why such enjoyment? Because it's not over the top as a football manga. Mizuki isn't crazy strong as to score by himself against any team. There's strategy in the story, and it's strategy developed by a girl, the manager Ubukata Chikako. She wanted to be a novelist and got criticised for her work, fell down and got right back up thanks to Tsukamoto's perseverance on the field. She's got real acumen for football and spends hours watching rival games to develop something for her team, unlike the real coach who's a bit useless on this front. So you have a fairly realistic story, a bit of drama but not too much, great characters and if you like football you will surely enjoy it. Another thing on Tsukamoto: the guy has no talent for shooting but somehow becomes a forward with his friend Kazama. Now that's interesting to me.
Thanks for reading.