I have to say, I was disappointed to see the exact same quests for Halloween having been active as last year. I didn't even get a pop up and my character got to do them all at once, and I got a duplicate Frankenbunny, same name and everything.
What about, say, a haunted house next year? Go in, have to solve puzzles, beat up ghosts and ghouls for a chance to win either a special mount or pet, or even gear? Maybe let people choose what they want by the path they take and each year they can try and win something different? That way it's not the same thing every year unless that's what they want. But they can only play it once per year.
Man I would love that. I would add, though, that if it was only possible to play it once a year - I'm assuming you mean you can't farm it for a few hours to try to get a certain drop - then drops for the mount or pet or whatever should be either guaranteed or very high. Imagine how frustrating it would be to go through the entire thing, not get that one item you really wanted, and not be able to try again for a full year, and even then, know that you probably wouldn't get the item!