Story: Haruhi Suzumiya has a very unique storyline- it wasn't completely what I was expecting, and quite frankly I don't think it even IS possible to know whats coming when you're a first-time viewer of this anime.
The story was never dull in this anime, it flowed beautifully and I really can't think of any issues with it- perhaps I would have liked more romance to develop, but if there was too much emphasis on the stereotypical and the normal trentds of storlines, I guess Suzumiya just wouldn't be the same. Some episodes had amazing endings (Episode six in particular was AMAZING)
The overall ending I found a little...odd. It didn't feel complete and it felt slightly random. The narration tied it up nicely, but the actual things happening on-screen I felt could have been a little better a conclusion. It felt slightly weak.
Animation: Also amazing. I can't fault it. Nothing went sloppy, nothing looked underdone, or overdone for that matter.
Sound: Not superbly memorable, but it all suited and was fitting.
Characters: Some of the mot memorable characters I've ever seen. Haruhi was an complete oddity, but suprisingly I didn't find her annoying like I do so many others remotely resembling her. You never knew what she'd be up to next and it made the show compelling. Kyon was another character who I thought I would dislike, but he was wholeheartedly likeable, making the show both amusing and sweet.
Mikuru was a character I wasn't completely keen on- the typical big breasted girl who is shy and used for fanservice, although for saying she was that awful stereotype I usually loathe, she still was mildly likeable, although it irritates me how people try to pair her off with Kyon. If she had more of a backbone I would like her properly. Itsuki was awesome :3 I don't know what it is abou him whats so great, but the mystery of him makes him a great character. Besides, how many anime characters manage to be mysterious and NICE? What happenned to the usual stereotyoe of mysterious and mean, like Kai from Beyblade and so many others? Itsuki made nice work. Yuki was very funny and unique.
Overall: Amazing. If you're hoping for romance you'll be let down, but other than that there seems to be some of everything in here. I definitely recommend it :)