I don't hate fantasy, but I don't love it either. I prefer fantasies of the Young Adult variety, such as Harry Potter. I'll admit that I have difficulties getting into the so-called epic fantasies. I abandoned The Sword of Truth series by the fourth book. I never started Lords of the Rings (watched the movie though). In my defense, I'm on page 10 of Games of Thrones (A Song of Ice and Fire), so there's hope for me yet.
I think different people dislike fantasies, especially of the epic variety, for different reasons such as:
Some readers prefer a more realistic world.
Fantasy, as a genre, pulls the reader the furthest away from reality out of all of the genres. It involves magic, sorcery, supernatural creatures, swords, horseriding, and castles. Some readers, living in the world of cars, computers, and iPhones, can't relate to the horse-and-carriage world. Nor can they imagine zapping things to life. The outlandish nature of fantasy novels is their appeal to many of its fans. Try as we may, we won't find a sword in a stone outside our apartment door. (Dammit.)
Just as there are people who like the stark contrast that many fantasy books pose to our reality, there are many people who don't. Some people may not have the skill of removing themselves from their experiences, limitations, and world and enter a fantastical environment. These readers are realists. Fantasy is for dreamers.
Other genres also pose similar problems, but fantasy is the most extreme in its outlandishness. At least contemporary and historical fiction have roots in their circumstances. Even science fiction holds some possibilities of the future. Fantasy doesn't have the slightest bit of chance of ever being realized. (Unless, of course, we somehow find out that humans have untapped magical powers that we've overlooked for millennia.)
Some may not like reading so many damn books.
Okay, I'm guilty of this one.
When I look at some of the major epic fantasy series, they span thousands of pages. The Sword of Truth totals 11 books. A Song of Ice and Fire has five books and counting. The Lord of the Rings trilogy, with a meager three books, is positively svelte in comparison.
That's a big commitment. Some marriages don't last as long as the time it takes to read one fantasy series.
Some people may resent the derivative and incestuous nature of fantasy books.
As others have mentioned, many epic fantasy books seem to copy each other. They're all set in the medieval times (except for Harry Potter, which proves my point). They all have dragons, elves, wizards, and witches. (Paranormal books also suffer from a overpopulation of vampires, shapeshifters, and werewolves.)
Some may feel like if they've read one, they've read them all. This isn't true, of course, but some just don't want to put in the effort of picking out the subtle differences between Terry Goodkind and Robert Jordan.
Some find the language typical of fantasy books inaccessible.
Hi K'zkhezen. Oh, hello S'kazen. Good-bye Trollopistickazjaky.
I'll say that the names go right into the ridiculous and unpronounceable. The same goes for names of cities, lands, and creatures in many fantasy books. Mordor was, thankfully, a simple name to remember. (Thumbs up to Tolkien).
Aside from the names, fantasy books tend to use flowery, descriptive prose. Fantasy writers do this because their worlds are so far removed from ours that they can't leave things sparsely described or the reader wouldn't be able to imagine these elves, basilisks, or weird creatures. This falls down to personal preference. Some may dislike the lengthy, descriptive, and flowery prose.
Oh, and it's really hard to remember all these damn names with one hundred characters to keep track of over thousands of pages. Gah!
Some people may think that fantasy is for nerds and geeks.
I was talking about this question with a friend, and he said something that I thought was true, sadly enough. For many people, when they think of "fantasy," they think of these hairy, fleece-wearing guys playing Dragons and Dungeons in the city park. They think of guys (ocassionally girls) sitting in their parent's basement reading Lord of the Rings for the 10th time.
Only recently has this perception changed. Now with Games of Thrones as one of the most popular TV shows and Lord of the Rings as one of the most successful movie franchises ever, people are realizing that fantasy isn't just for nerds. Fantasy is about magic and dreaming, not mouth-breathing, overgrown boys with poor hygiene.
Of course, this is an utterly unfair stereotype, especially since there are more sub-genres of fantasies other than epic, especially with Harry Potter's successes. Not only that, fantasy fans come in all shapes, sizes, and genders. But the world is full of unfair stereotypes.
In a way, fantasy is a lifestyle. You're either all the way into it --you've read George R. R. Martin, Terry Goodkind, Robert Jordan, J. R. R. Tolkein, Ursula Le Guin -- or you're not. Fantasy is a great genre, but it isn't for everyone, with its complicated names, twisty plots, massive page-count, and total lack of realism.
More questions on fantasy: