It goes without saying that magic forms an integral part of the fantasy setting. But I am curious as to what preferences people have towards the nature of magic in your games and why. People certainly have their preferences and expectations regarding magic.
Do you prefer magic that is distinctly delineated by source (i.e., arcane vs. divine vs. psionic), or do you prefer singular unified magic systems? Do you prefer Vancian magic or some other spellcasting method? Is magic prevalent or rare? Is it easily accessible to learn or is it a painstaking enterprise? Is it earth-shattering or subtle? Is it benign or malignant? Is magic metaphysically explainable or is it utterly mysterious? Is magic treated as a technological tool or as a chaotic force? How do magic-users view magic? How do non-magic-users view magic? Or perhaps it falls somewhere between all these or in other aspects that I did not include.
In short, how do you prefer magic to exist in your games?
As a player, I'm fine with the premise of the system or game we happen to be playing in. But, when I DM, I prefer to use my houseruled system for everything. Any adventure or genre I'm using, I'll adapt it to my system or my system to it. But as concerns magic and your questions, here's my answers:
I prefer a singular unified magic system. Magic is simply the mind focusing and manipulating the energies of the universe. Sources like Arcane, Divine, and Psionic, simply define
where that energy comes from. But in the end, the energy and what it does is the same...whether Arcane, Divine, or Psionic.
I despise Vancian magic. (edit): At least unless it was in a campaign based on The Dying Earth series.

In generic fantasy though, IMO it doesn't make logical sense, and simply stands out as a huge gamist construct to me. (end edit) I prefer a mostly at-will type system, so that magic works more like The Force in the Star Wars movies (but not in the RPG books).
Magic is prevalent and rare. Prevalent in that it's everywhere, it's the very fabric of the Universe. Rare in that very few people ever learn to sense it, let alone manipulate it.
Magic is both a painstaking thing to learn to use, and an accessable thing. It's accesable in that a player character can learn it and use it in just as equitable a manner as a Warrior can learn and use their combat skills. But, as far as my campaign world, Magic Users are extremely rare (so rare that they are mostly considered Myth).
Magic can be both Earth-shattering and subtle, both benign and malevolant...based entirely on the individual caster.
To a magic user, magic is an art and a science. Magic has mystery even to a caster, but also has a science and methodology to it's use. However, to a non-magic user, magic is completely mysterious.
