I love this series. It's hard to say why; it isn't very popular and there isn't anything special about it. There is the typical hot-blooded shounen hero who is a little ehh... on the IQ scale but is actually a hidden genius at the game and his dark-haired talented rival who initially clash in everything but gradually realises that they have things in common and work extremely well together to pulverise their enemies. Oh, and in true sport manga fashion, they are the underdogs. Does it sound a bit familiar?
So, my point is, there isn't much to differentiate it from the rest of the sports manga aside from the fact that it's about volleyball which is considerably rare compared to all the baseball mangas that are a dime a dozen. But nevertheless Haikyuu!! is a manga that I look forward to reading, suffer heart problems when there isn't any new chapters, and fangirl immensely over cool scenes.
Why? Like I said at the start, it's hard to say. It has nothing in particular that stands out from the crowd, but what it does have is simply a combination of little things that works, and works very well. There's just something about it that makes you feel good. The cliched talks and speeches and one liners makes me inspired instead of wanting to groan and shout for them to get along with it, the comedy actually makes me laugh and the characters are all so likeable! Plus, some (important) matches are done in like four or five chapters! Do you know how much of a miracle that is? Do you know how weird that is, how strange, how praise-worthy? I have read my fair share of sports manga and let me tell you, NO (important) MATCHES ARE DONE IN MERELY FOUR/FIVE CHAPTERS! There is one particular manga called Rookies whose matches can drag on for twenty-odd chapters. Can you imagine the pain in slogging through them? (I would recommend reading it anyway fyi)
I have nothing to entice you to read Haikyuu!! except for my whole hearted recommendation that this is great which I can't back it with actual proof but man, you've got to read it!
Also, Furudate Haruichi really knows how to make things cool. There are some important scenes where the pose, the angle, the facial expression and all-round awesomeness just made me stop for a moment and seriously fangirl.