Personally, I found One Punch Man a blast to watch, but there are some definite flaws with it. For some reason, I feel like going over the bad parts first, instead of starting off well.
Cons:
-Lack of deep characterization: Saitama is great, but none of the main or side characters are not developed well. Many characters are introduced and the viewer can be impressed by their awesome powers, but we do not get a good insight into what makes them tick.
-How far does the anime take the parody? : One Punch Man is a parody of the shounen/superhero anime, but how much does the anime try to embrace its tropes? Near the end, I felt that the comedy and the sheer stupidity of its plot were reaching a peak where I could not intake the vast quantities and scale of its over the top and exaggerated features. This also comes from the fact that many characters on the protagonist's team and the main character himself are so overpowered that there is a lack of tension in fights sometimes.
-Mundane, slightly boring moments between action scenes: Sometimes, I found myself a bit bored by the everyday moments of Saitama. I am normally fine with these types of regular life, but One Punch Man's ones did not appeal to me.
Pros:
Great art: Madhouse produces very consistent and above average art. The characters look great and the city backgrounds are very nostalgic, reminding me of a superhero city.
Amazing action: The action in One Punch Man is scary good. When Saitama is not completely destroying people, there can be incredible fight scenes that can fill viewers with passion and fire within their hearts. These moments will glue people to their screens. The viewing angles and the style is adrenaline pumping and helps make the action just breathtaking. Genos and other side characters provide superb visuals for explosions and other powerful attacks.
Great OP: Old-fashioned, purely passionate and powerful song, just makes you want to punch through 15 walls
Good comedy: Saitama's jokes work really well, as he completely destroys the serious tone of certain parts of the anime.
Overall: 9/10 a great parody of action anime that has godly action scenes, but has comedy and tropes that may get stale
