Let's take a look at the world part of the story first. It could be the world we know and are familiar with, only with magic behind the scenes (or not), or it could be something completely new, created from scratch by the author. One of my favorite examples of this is, that I've read recently anyway, (of course) the Shadowmarch series by Tad Williams. (Forgive me talking about him so much in these posts, I just really like his books. *shrugs*). He started from scratch and made up, not only a kingdom, but a whole world filled with gods and demigods, human characters, and various forms of magical/mythical beings. Writers who create new worlds go through quite a bit of work to make it happen. I for one love to do it. I have created new worlds multiple times in my WIPs. It can be daunting and sometimes hard to figure out all the details needed, but in the end it's always worth it. To me anyway... When a writer creates a new world they have the opportunity to go beyond the boundaries set for them by the world we live in. There are limits, of sorts, that come with writing about our world. But when you create a new one, there are no restraints. Granted, it has to be somewhat plausible, but there is far more room to move when you can create everything down to the tiniest detail; make it all your own design.
Another thing I love about the world aspect is jumping back and forth. In Stephen King's The Dark Tower series, he has his own little world, or rather ours but one that has "moved on". But, Roland, the MC, travels from Mid-World to our world... a few times actually, and he's not the only one. By means of portals and doorways they are transported to different times and places in our world. (Insert King into his own work during two of these excursions, which some people think is arrogant, but I adore. He did it quite well IMHO.) Other characters are transported in different ways, in some cases death, from our world to Mid-World. Being able to see a character go back and forth between the two worlds allows you to see not only their world, but to see ours from a perspective we have never had. Things that are commonplace to us are alien to them, and would be the same if we were to travel to their world. That's what does it for me, right there. To be able to not only jump into a place I've never been before, but to know what our world looks like to an outsider, is what appeals to me.
The Powers:Another thing I adore about writing in Fantasy is the power aspect. Call them powers, gifts, abilities, whatever you want. The point is, they're fun to play with and enormous fun to dole out IMHO. For example; I have one MC who can do multiple things like control the elements, telekinesis, telepathy, etc. (the girl is a veritable fortress of power), and then I have some with only one or two powers. FYI: pretty much all of my MC's are witches, and female ones at that. I do have some that aren't strictly witches and some that are male, but for the most part, that's what I write. The one male I am truly in love with, and he stars in three of my WIPs, is simple really; he has only two powers and he kicks major ass with them, so I don't find it necessary to give him more. As for the one with multiple powers, she has to have them, it's all part and parcel of the life she's living inside my head. She also kicks major ass. ;-)
But when you start to look at all of the possibilities for powers out there, you'll find a very wide range. I'd be surprised to find there are limits to what you can make your characters do. I suppose I should allow that some people will say there are limits, but not for me, not in my work. I mean, think about it. You can make a character so powerful that he/she can wipe out an entire legion of evil beings with the swipe of their hand. Or you can just keep it simple, give the MC just the basics and watch them tear the world apart. ;-)
Ah, now here's where I really get long-winded and rambly. The plots, the plots, the plots. Love 'em. Not always mind you, there are some books I've read that I wished I'd never even heard of, but for the most part I do love them. Of course the plot is essential to any story, that's just a given. But what I'm referring to is the fact that pretty much every story has been told by now, it's the ways they are reinvented that really excite me. Who hasn't read various "chosen one" scenarios or the whole apocalypse idea over and over again? But why do we keep reading these stories that, at the core, are all the same? We do it because the author has the ability to make their story different from all the other ones out there. We do it because the author is able to take an old idea and put a new twist on it. Let's talk Harry Potter for a moment. Another "chosen one" situation, but done different than the rest by the tiniest details that make up the characters, the setting, the trials, etc. Inevitably one side is going to win in these battles, and it's not always the good side either. In my reading experiences, which admittedly is much less than many people I associate with, I have found that I like these chosen one stories that deal with the younger generation. Depending on how long these things go on for, years in the case of HP, we may get to see the character grow and develop, either into who everyone thinks they should, or into the polar opposite of that. After all, the chosen one doesn't always turn out good... or even begin that way. Watching how the character deals with the burden on their shoulders is also another appealing thing to me. It makes me wonder how I would cope if I were ever in the same situation. Though, I will say, it wouldn't be nearly as well as they do. :-D
How many times have we read a book where the fate of the world rested on the MC's, and possibly supporting character's, shoulders? I have done this a few times myself. The appeal for the end of the world scenario, to me anyway, is to see how the MC overcomes it all to win in the end....or not. There's a 50-50 chance that things will not go the way they should, i.e. HEA or at least the best HEA possible.
There's also a chance the world will crumble and fall, taking every inhabitant along with it. Don't ya just love it? There is also to consider, if the apocalypse is averted, the aftermath of such a battle. What does it do to our everyday lives? What does it do to those who, thinking magic is nothing but fairy tale and legend, see it firsthand and must live with the knowledge of something they've never faced before? Not only that, but let's say the MC survives the whole ordeal, how do they go on afterward? What do they do now that, in some cases, their destiny or purpose is complete?
Now, I know you don't always get the answers to every question you have when you read a book. Sometimes you're left scratching your head and wanting to give anything just to get more information. But that's the beauty of it. If a story can leave you wanting more it's more than worth it in the end. You may be frustrated with the way the story ends, you may not agree with what happens, but that's just the way it goes. If with your story you can manage to bring your reader into your world, make them feel like they are living through the same experiences as your MC, and sometimes even make them want to be your MC, then IMHO you've written an excellent Fantasy story. Even if your preferred genre is not Fantasy, I would recommend giving it a shot at least once. You never know what's going to come of it.