Okay, I'll probably get lynched for this post, but here goes.
I recently finished this series. Yeah, it was funny, the animation was good, the story was... different, and the characters were interesting. But, I will not lie, I found the theme song to be completely terrible and extremely annoying. Other than the OP, I thought it was pretty good, and worthy of a 7, or even possibly an 8, out of 10. But, honestly, what's so great about the show? I watched the whole thing, laughing occasionally, but could never really understand what people find so amazing about it.
Of course, my "tastes" in anime are quite peculiar compared to most of this forum's users (and even the internet in general). I thought that Lucky Star was boring, unfunny trash that got by on cuteness alone, and that Elfen Lied was nothing more than over-hyped, glorified guro lolicon with uninteresting characters and a cookie-cutter story.
I'm not saying this to bash any of the shows, or their respective fans, I'm simply stating my opinion. However, if anyone would like to tell me why The Melancholy of Haruhi Suzumiya is so great, I'd be glad to hear your opinion.