The story starts off in a pretty stupid way and things remain pretty stupid throughout. The demon lord is a really whimsy guy that wants to destroy the human world, but he's too lazy to do it himself. It'd probably take him all of 5 seconds to do it. Stupid... A good kind of stupid that makes you laugh at just how absurd it is. A naked baby that just clings onto Oga's back? A person being driven into a wall with just their ass out and legs hanging down? This manga's full of weird stuff like that, and that gives it a certain charm of its own.

The art is pretty average; not bad, but not amazing. It has its own unique quirks, though, like the blank stare characters get when they find something unbelievable. I'm not a fan of fan service, so I don't really like the way Hilda dresses or her large breasts, and she happens to be in almost every chapter. Kunieda, the other main female character, has a far more modest appearance, though. Hilda also seems a little more modest in later chapters, I suppose.

I feared the story would take a "demon world" turn and become less interesting like YuYu Hakusho and Bleach did. I think a human world and casual setting is more interesting. Thankfully, Beelzebub does the "demon world" thing in moderation.
As the story progresses, lots of needless characters are added and we even delve into their personal lives at times. The story kinda loses its focus as Oga and Beel adapt to each other. Sometimes it feels like a really typical manga series that some anime fanatic would think up. I thought 7/10 would be fitting enough, but there's one thing in this story that gives it that extra point - Furuichi.
Furuichi is a pretty cool and attractive character, as well as a voice of reason. For a long time, he was the only character in the story that didn't fight. Not because of his coolness, but because he's just plain weak. He's gradually walked on to the point that he's the butt end of all jokes, no longer a respectable character in any form. Everything about Furuichi is hilarious.

Overall, this manga is pretty enjoyable and unique in its own ways. It generally avoids being too serious, so it's often fun and funny. It's a little typical at times, but not disappointing. I can't recall ever finding it to be too dull or anything.