4.5 Stars.
If the art were of a consistently higher quality, I think this series would get a lot more attention. This manga is everything one could want from this genre, in my opinion.
The guy doesn't get any kind of special abilities or gear... all he has is the ability to do is practice karate. If he takes damage, there's a consequence. This character is never complacent and always feels mature, rational, and careful when acting. His dynamic with Puppy, a companion recruited in Volume 8, is a tried-and-true classic done well. The way that the killing of monster and human alike haunts the MC reminds me a lot of Thorfinn's guilt.
Every story arc feels complete and events actually have a purpose. I really enjoyed the bit with the town full of those who failed to break the level barrier. There are some side characters that I found had really great motivations and stories. I do wish that they explored some concepts further, but what's there is still effective enough.
There's a nice moment where it's revealed a skill of the MC's, which enhances his senses, has caused him to become addicted to the mana added to food... perfect set-up for a legitimate-feeling leap in strength on the his part after overcoming the dependency.