Awful. Just horribly, horribly, mind-numbingly awful. That's basically how I'd describe volume 1 of the 'Melancholy of Haruhi Suzumiya' manga adaptation [NB: what everyone else has been saying - the hardcover option here is the light novel, which is amazing].
Basically, I came into Haruhi Suzumiya pretty fresh. I picked up the light novel on a whim, knowing next to nothing about it, and loved it. Afterwards I decided to read the manga as well, intending to watch the anime after that. Let me tell you, the manga nearly killed that idea. Everything about it is terrible. It's like a textbook on how not to make something classified as 'entertainment'.
Let's see: the illustrations are awful, and look nothing like Noizi Ito's light novel illustrations, nor the anime (which I eventually decided to watch anyway... thank god, because it's awesome). Not only are the characters way off, especially Kyon, but the panels do not flow at all. Absolutely zero narrative is conveyed pictorially. I had to use my prior knowledge of the storyline to fill in like 80% of the storyline.
Picking apart an English translation of a manga is always risky, because obviously a lot is lost in translation. Still, the text we have here is just... basically like somebody auto-summarized the light novel, and picked out random half-sentences that sometimes (... sometimes) correspond with the illustrations. 1% of the individual depth of the characters is communicated. The story you get is a sort of Haruhi-lite edition... as if somebody had recounted the light novel/anime's basic plot to a friend, and that friend told another friend, and then that friend told another friend, and that friend opened up an IM window with you and spewed out a vague semblance of the plot he remembered.
So, yeah, in summary. Light novels (I've read the first 3): GREAT. Anime (I've watched the first season): GREAT. Manga (I also read volume two): SPITEFUL. Almost a crime against humanity. I'm only giving it two stars because, as it contains hints of the original storyline, it can't be considered a total, absolute loss. Because I'm a sucker idiot, I went out and purchased the next 4 volumes of the manga. The covers look nice, at least (yes, that's the manga cover on this amazon item page). I'm hoping it might get better. Hmm...