It's hard to say, really. With some of my favorites, or-more importantly-with first time reads I really get into, in the fantasy genre, endings always seem to be bittersweet. Sweet, because the characters who struggled to get done what they needed to, and finally be able to settle down for peace, but bitter because I realize I can't turn the page and see more of what's going on.
I would say some examples of this for me would probably be things like Soldier Son trilogy by Robin Hobb and The Interior Life: A Quest by Katherine Blake. (The latter I definitely recommend reading, by the way. It is thoroughly enjoyable.)
Some books I disliked so much, or were simply annoyed by so much for some reason, I couldn't wait for them to end. The Memory, Sorrow, and Thorn series by Tad Williams belongs in this sort of category, not because the story he was telling was bad, but because the POVs between characters bounced around more than Flubber on speed.
Other reads I tend to favorite seem to be simple, goodhearted fun, and while it can be sad for those to end, it's not as bad as more intense reads. Dark Castle, White Horse by Tanith Lee is a good example of such a category.