[Reviewed at chapter 25]
Honestly, this was a very annoying manga to read. I do not like the MC - he's stupid and a bit mental (although that might be deliberate as other characters think the same). He constantly obsess over his presence, instead of taking advantage of his stealth to fight monsters. The supporting characters do not do much nor have much of a story line so you don't really care much about them, and honestly, some of them are just as annoying as the MC (like the shop keeper)
The biggest issue I have is with the way the leveling works. OP kills thousands of monsters and still remains at G rank, he only moves up to F rank after killing over 10,000 monsters, which is ridiculous - in other manga you only need to do a few herb gathering quests to rank up from G to F. And although he's depicted as "leveling up" quite frequently, most of his skill points still remain at like 1 or 2, which doesn't add up - what exactly is going on with his level ups? It's never explained properly. The most ridiculous thing is that his main skill is supposed to be a growth skill that makes him gain much more exp compared to others, but this isn't reflected in his stats. 25 chapters in, he's still just at rank F.
The other major issue I have is the "villains pick on girl" arc. [Spoilers ahead]
So these guys set up a trap for MC and proceed to kill him but it backfires due to a monster flood. Suddenly all is forgiven and MC is trying to help them, ends up failing and then blames himself for not being able to save them.. like wtf, why would he have any sort of empathy for SCUM who were about to r**e the girl and murder both of them? And its not like the MC has some good history with them, every encounter with the bad guys has shown that they were scum, lowest of the low, who don't deserve any mercy. They were already given a chance to reform when they were first caught by the police, but instead they were set free. None of this makes any sense.
Overall, the MC isn't likeable at all, he makes this poorly-drawn stupid face all the time and he's mental. All that being said, it wasn't enough for me to drop the manga as I'm a bit invested in the growth of the MC and want to see if he gets any better.