One Punch Man!? Straight 10's across the board. Why!? Because it's awesome. I don't know how anyone couldn't like this anime honestly.
Storyline: A hero that kills everything in one punch, but truly just wishes he could find an enemy who can take more then one punch from him? It's so simply and yet it's so enjoyable.
Characters: All the characters are precious in their own way. Specially Saitama.
Art & Sounds: The art... is absolutely insane. I can't even begin to describe how intense the fights are and how crazy the art is. Take 5 minutes to just watch one fight on youtube and you'll definitely be hooked. The sound is just as great, the publishers of this anime have done such an amazing job on the art and sound for this anime.
My Final Conclusion: Everyone should see this anime, seriously. Not much else I can say. Go now... watch it and bask in it's glory.