The stories are good, the animation is good, the voice acting is good. The character of Ben is not good. He's rude, self-centered, narcissistic, self-absorbed, arrogant, argumentative, impulsive, and acts rather stupidly in dire situations. In short, he has few, if any, redeeming qualities or characteristics. While the other characters change and grow to a greater or lesser extent, Ben does not. He is not a reasonable role model by any stretch of imagination, especially for boys from 9 to13, the target audience for the show. Gwen on the other hand show grace and growth and would be a very acceptable role model for both boys and girls in that age range. If parents watch with their children, they might do well to point out Ben's character flaws, and emphasize better solutions and responses for them.
As always, this is just my opinion and your mileage may vary.
As always, this is just my opinion and your mileage may vary.