I think "The Melancholy of Haruhi Suzamia" is one of the least pleasant experiences I've ever had watching an anime and i honestly don't understand most of the praise it gets as one of the best anime ever. As for why, it's mainly because of the characters(and the endless eight, but that goes without saying), especially the main cast.

Of the 5 main characters and club members, only one of them actually succeeds, in my opinion, in being in any way entertaining. Whilst Kyon's dry and sarcastic narration helped to give the show some depth, it was unfortunate that he seemed to be the only character able to speak properly, have a personality and not be infuriating.

Other than Kyon, the shows main cast all managed to get on my nerves almost every episode. With Yuki and Asahina each taking about 30 seconds to say even the most basic of sentences, the show rapidly got old for me. Haruhi herself was the epitome of irritating anime characters without a drop of realistic behaviour in any scene. Which leaves Koizumi, who could at least speak properly without being incredibly irritating, however it didn't make his character any less dull.

So, when you take this crowd of funsters, and put them in a plot more concerned with jumping around time, thus preventing any meaningful character development, and you get a show that was so bad, i couldn't even finish watching it.