Unfortunately, having seen the anime first, I feel that the first volume of the original light novels offers little additional insight to the characters and their situations as the anime was such a faithful adaptation. Many lines from the anime were apparently lifted directly out of the book. Also, because I watched the anime first, I can't help but compare it to the book.
As a light novel, The Melancholy of Haruhi Suzumiya
is a funny and entertaining read. I did pick up on some details that I didn't notice in the anime, but I think that's mainly because I was too engaged in trying to figure out the disjointed timeline of the anime (the mixed up episode order). The book follows a traditional narrative style-- as in, beginning, middle, and end in order-- so things were much easier to take in.
I do think the scientific explanations were rather dull and poorly thought out, as if they were just thrown in there to justify the storyline (that Haruhi was some kind of powerful being), but luckily there are only a few short instances of it and once they were done with, the story goes on in its fun, light-hearted way.
But The Melancholy of Haruhi Suzumiya
is more than just a fun, light-hearted high school comedy. What really struck while reading this, which I never realized while watching the anime, was that the story is essentially about longing. Both Haruhi and Kyon long for the extraordinary. As much as Kyon complains about Haruhi and the SOS Brigade, I think deep down, he really wants to be there. I see his dry sarcasm and his complaints as his way of trying to rationalize the strange things that are occurring around him-- his childhood hopes of meeting aliens, time travellers, and espers never came true, so he's rather cautious of getting his hopes up this time.
Haruhi, on the other hand, was a character I never really liked in the anime. She seemed really bossy and self-centred, which, admittedly, she still is in the light novel. That hasn't changed. But what has changed is my understanding of her. She was someone who was done with sitting around waiting for things to happen to her. If mysterious things don't come to her, she'll just have to go to them. It is with this philosophy that she starts up the SOS Brigade and it is this that I've come to like about her. There's just something admirable about a person who is willing to make things happen (her methods are certainly questionable, but you have to admire her spirit). This isn't any different from the anime and I don't know why I didn't realize this until now. Maybe consuming the story in text form made the difference.