For the most part, The World God Only Knows is a very formulaic series based around the idea of a gamer capturing the hearts of real life women in the form of a Dating Sim game. Even by the time of the Goddess chapters, it still stayed relatively the same formula except that it gave the manga a chance to actually develop some of the girls introduced from the previous character arcs.
It was only by the time of the Heart of Jupiter chapters that the series delves into something completely different. And while this wasn't "bad," it can feel very out-of-place. A lot of folk even admit that they see the final Goddess chapter as being the actual ending of the series, because the Heart of Jupiter chapters just didn't feel right for what this manga was.
...and speaking of the ending. It was rushed as all get-out. Just look at some of the YMMV examples for the series here, and you'll see the loads of problems the ending got with some readers; the biggest one being that there was never a true final battle to end the threat of Satyr.