What kind of fantasy is this? Is it the ideal world I'd want to live in? A fantasy setting I think would be fun? Or sex fantasy?
I can't think of much to say for a fantasy setting, if I could come up with a good/original one I'd be writing it. And I would be a person with a completely different set of skills.
The sex fantasy? It involves identical twins, and cheesecake, and that's all I'm saying.
So, the ideal world...
Well, there's an afterlife that's just like the world of the living in many respects, after dying you get reborn in the next one, and they keep going until the 7th recursion (seven because it's a nice number for this kind of thing). After that, you get born back into this world. You can't get born as anything non-sapient, and if you're "only mostly dead" (e.g. if you're cryogenically frozen, or anything vaguely similar that would imply it's not a final death) you don't get moved on, and instead you just skip ahead to whenever you get rezzed (or your cryonics tube gets blown up and you move on then). When you're in limbo, you don't experience anything so the time passes by instantaneously.
And with that done, let's move on to the world itself: Relativity goes out the window, gets loads of glass embedded in it, and makes an unpleasant sound when it hits the pavement three floors below. Lightspeed is still the limit for conventional travel, but warp drive isn't even difficult to design or build, and the FTL travel that ensues *somehow* doesn't result in FTL travel. We make physicists cry even more by invoking the possibility of reactors that generate energy from nothing (but only at a very slight margin - in anything less than the insanely long long-term, every single energy source we have is more cost-effective). The expansion of the universe slows way the f--k down, and begins moving at a rate exactly proportional to the increase in energy in the universe due to these reactors, to keep the mass/energy density the same for the rest of eternity. Also, we get time travel (not caused by the warp drives, the universe is robust against paradoxes but you can still change things, but you don't get to use the butterfly effect and make various massive changes) and antigravity (reducing something to 1/10th its weight is possible and can easily be used for rockets and skyscrapers, mass remains constant).
It's possible for civilizations to ascend to another plane of existence, and when one does it makes its own universe that splits from our own. Higher beings very rarely interfere with the mortal universes, and ascending like this is pretty much inevitable for any civilization that gets sufficiently advanced, with the exception of less advanced groups that splinter away. The previously-occupied planets are simply left behind, unoccupied.
99% of solar systems for which a "habitable zone" could be said to exist have a planet occupying that space, including multiple-star systems, red dwarfs, red giants, etcetera etcetera.
These changes would be made with the laws of physics as we know them, and the way the world we live in works without those technologies active, staying as close to how they are now as they can possibly get. The real physics-breakage is the next bit:
Everyone gets superpowers. On top of a degree of super-durability, everyone gets a special ability that meshes with their personality, which won't be completely unique (because a power unique enough to be a one-in-seven-billion thing is probably niche enough that it sucks ass) but will be pretty rare. Let's say there's only a ten percent chance that any of the people you know personally will have the same kind of power, and even then there'll be minor differences like in the exact colour of the eye beams you can shoot. These powers would all be balanced perfectly against each other, and the power level would be truly superhuman, but not as powerful as most actual superheroes tend to be. About halfway between that, and the amount of talent implied by an MLP cutie mark, basically, and the power you have would be about as related to your personality as the latter would be. I'm not really sure how to specify this power level all that precisely, but I think you know what I mean.
Oh, obviously I'd be an exception to this rule, since this is my show - my power would tip the balance, I think I'll go with the ability to do a mitosis-like thing that results in clones of me, who can merge at a later date so that there's only one me again, and he has all of the memories the clones had combined. The limit for people on the normal power level would, I think, be to just split once, but my power would allow four rounds of division (so up to 16 clones active at once) before the power needs to be recharged by merging.
Okay, there might be a few other things, but I think this is enough to make the world a) a nice place and b) exciting and adventure-friendly. So that's enough for me.
This would probably be my first wish if I got wishes from a genie(I'd do quite a bit of preparation so I can say it all in one go without loopholes making the universe grimdark). Then my next wish would be for a great big adventure to come and get me, complete with Manic Pixie Dream Girl(/s), Evil Masterminds, and all kinds of other tropes in full swing. Third wish would be to make myself forget about the genie, so that the whole thing becomes surprising and awesome and I never have to angst about having been the creator of the supervillain and various related existential worries.