This has ended up being insanely long, so before we get started, I'll summarize this in a TLDR:
Like fantasy? Like laughing your ass off? Read Terry Pratchett. You'll wonder why you didn't sooner.
When I say "Discworld", what do you think of? If your answer's not "the best long-running fantasy humor series in the world", then get yourself to a bookstore, head to the Sci-Fi/Fantasy section and look under P. Somewhere in there is Sir Terry Pratchett and his simply superb series, the saga of Discworld. Starting with The Colour of Magic and running up to his newest release in October, Snuff, Sir Terry (Yes, he's knighted) has spent over three decades amusing the world with the hilarious adventures of various people living on a flat disc of a world (hence, Discworld), balanced on the backs of four elephants who in turn stand on the back of the Great A'Tuin, an enormous turtle swimming through endless space. And they know this for a fact because they've gone down there and looked.
I've read hundred of books over my life, and not a single one has come close to the way Pratchett makes his characters live, makes you laugh, and weaves flavors of the real world into a fantasy one so well. Everywhere you look in his books, there's a reference to something you know, and if you don't know it, then someday, you'll be somewhere or read something and realize "Wait a second...!" For having over 30 books in a single series, he also makes them some of the easiest books to pick up and read I've ever seen. You can pick up any book in any of the storylines and start reading, and you won't feel like you needed to have read the previous ones to understand what happening. However, you will end up WANTING to read the previous ones.
I'd go into detail about the characters, but frankly there are too many, and you can't just summarize a cast as vibrant and color as the people of Discworld. How many fantasy adventures have you read where the main characters who save the day are old women? His witches, Granny Weatherwax and Nanny Ogg, do it time and time again, and they kick ass while they're at it if they have to. Think the world, history, and life as we know it can be saved by an incompetent, cowardly wizard, the world's first tourist, and a trunk with a hundred legs and bottomless appetite? If there's a magical mess, Rincewind and Twoflower are almost always found in the middle of it, with Rincewind making a manic dash for the end and Twoflower taking pictures of the mess that's coming. How about a thief who's being blackmailed by a congenial tyrant into reforming public services anyway he can think of how? Moist von Lipwig does it in Going Postal and Making Money. And all the while, the most ragtag Night Watch in the world, made up of humans (including one who has letter certifying that he is, in fact, human), dwarves, trolls, vampires, werewolves, and a zombie, led by a human who was raised by dwarves, are hard at work protecting their city and their own by any means necessary. Even Death, yes the skeleton in the black cowl with a scythe, has his own stories (and is the most prolific character, appearing at least once in every book). And really, that's not even everyone. There are several once-offs and other storylines I haven't even mentioned, and countless other minor characters you'll see throughout each storyline (such as the Librarian. He was a man. Now he's an orangutan. Whatever you do, don't call him a monkey) and yet, despite there being dozens of names and faces that show up time and time again, they all have their own personalities, their own stories, you're thrilled when they make it through their next challenge and sad if they don't (hey, Death doesn't just hang around for no reason...except for with Rincewind.) You get to know them all as well as your own family, and you're sad when there's no more book to read.
I couldn't tell you how many years ago it was the DM handed me Guards! Guards! and told me to give it a read. It didn't win my interest, honestly. Then, I read Making Money and was actually hooked. Since then, I've read all but one Discworld book, and reread Guards! Guards! (I liked it MUCH better when I knew the characters and fully understood what was happening). Hands down, it's my favorite series, and I can't describe the admiration I have for Sir Terry, as a writer and as a person. A few years ago, my favorite author was diagnosed with early onset Alzheimer's. A few years later, he's continuing to write and says he still has at least two more stories in him. As well as writing, he's still traveling, sharing with the world his encouragement for assisted death, and it feels like he's getting things done, or at least raising awareness. He hasn't let a diagnosis stop him at all. I don't know if I could be as strong as he gives the appearance of being with such a horrible diagnosis, but if it happened to me, I know who I would look up to for the strength to keep going. I already look up to him as an aspiring fantasy writer, and hope that maybe, someday, I'll have the chance to meet him before it's too late.