Shijou Saikyou no Deshi Kenichi could have been easily a 9/10 for me, but sadly I had to give only 7/10.
We follow the story of Kenichi, who is a weakling at first but want to become stronger in order to be able to protect the people around him. Therefore there is a lot of training in his life. His masters make the training hell for him, but enjoyable for the readers. Kenichi eventually finds himself in dire situations, where he need to fight stronger and stronger opponents. So basically Kenichi's story is a generic shounen manga with a little humour in it. But what makes it good?
Characters:
Kenichi is a talentless martial artist, which is rare for this kind of stories. The people around him, all of them have interesting personalities and well-written backstories. Kenichi and also his friends are all have something to live for. For Kenichi is to protect Miu, for other characters is to be the strongest, or just make all the fat people around the world proud of themselves, no matter what, they try to achieve that goal. What I personally really liked, is the masters. I think I can say they are the best masters I have seen so far, they train Kenichi really hard, it can be called almost a torture, but they do this because they care about him. Al of the masters train Kenichi in a different way, and not just in a physical way. Even the reader can learn a lot from this masters philosophy. Kenichi's friends are also well written, most of them were enemies before, but this makes them even more loveable, and the story even better.
Art:
It is not astonishing, or the best I have ever seen, but it is decent. What deserves a special compliment is the fight scenes. The fights are well drawn and organized, easy to follow whats happening. There are a good amount of details in the characters, past and mid-fight injuries are nicely drawn. You can see Kenichi's body development throughout the manga, he slowly becomes more and more buffed. For comedic release there are a good amount of times when the characters are drawn in a minimal comedic way, it represents the lightheartedness of the situations really good.
Humour:
Most of the jokes come from the fact that Kenichi is talentless, but we can find small funny gags here and there in a great number. It is more of a fighting manga than a comedy manga, but it is still a good portion of it, and I have to say that there were a good amount of times when it made me laugh.

So what was bad in Shijou Saikyou no Deshi Kenichi?
My biggest problem in this manga was the overdone fanservice and the asspulled story.
Fanservice:
Dont'get me wrong, I don't mind fanservice at all, a little naked time here and there is ok, but this manga had too much. At the beginning of the story there was little to none fan service, but somewhere in the middle of the story something changed, and it became like 60% fanservice, which is too much. And when I am saying 60%, I mean there are chapters(not just one), where female characters fighting literally naked. At the end of the story I knew at the beginning of a fight, if there is at least one female character, she will be stripped down at the end of the fight. I wouldn't mind it at all if it wasn't forced. Instead of a good story, the author tried to keep the readers with fanservice.
The second half of the Story:
Same as with the fanservice. At the first half of the manga, the story was good and interesting. Kenichi was developing, becoming stronger, and getting in more and more dangerous situations. The fights were good and interesting. New, unique and interesting characters kept popping up. But somewhere in the middle, maybe somewhere between 200 and 300, something went wrong. The story itself started to get worse and worse. At the last arcs, the story had so many asspulls, it was almost unpleasant to read. I read it because it still had its good moments, but with the bad writing and the too much fanservice, it became bad. I guess the author put all his efforts to make fanservice, and he had no timeenergy left to actually think about the story. Kenichi could have been so much more.
Ending:
It has an ending, so it is officially finished, which is better than a sudden stop, but it was a bit rushed, and there are some questions which remain unanswered.

+1 (little spoiler): I don't want to consider it as a bad thing in this manga, it is more like a generic problem, but the romance in this story is unsatisfying. We get our MC to run after a girl through almost 600 chapters, and we get nearly nothing. We know they have feelings, but there is basically no development. There are a couple good moments, but that is all we got.

Overall:
With its flaws, Kenichi is still a manga worth reading, especially the first half. If you want to stop at the point where it is still good, stop after the D of D.