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Stay away from those Game's children. They're the gateway to the Devil !!!! "
What is Magic ? Is it card tricks or men escaping from locked water tanks ? Is it the twinkle in someone's eye ? Is it Goth chicks acting out scenes from Buffy the Vampire Slayer, thinking one day they'll be like Willow ? Well avoiding Hollywoods marketing ploys....
Magic is the unknown. That what can not be explained.
& a way to sell books called wicka or something.
Yes I'm ignoring the Wiki definition... Most likely made by fat guys who wear black silk & call themselves Lastat.
Science & technology in a time before explanation or understanding may have been called magic. Anything that lacks understanding or logical pattern can be magic. If I were to pick two words for magic: Uncomprehending & Uncontrollable.
Looking at all the video games I've played over the year,
Not one has magic, & I've played a lot of RPG's. Video game magic is clearly defined & understood. They're not really spells, more like invisible gun clips. A fireball spell is really a Grenade. Mana for most attack spells are just like gun clips or a quiver of Arrows.
Still nothing more clearly effects a game & sometimes defines it by it's view of magic. All types of players play games for what they can not do in real life, & magic is mascot of these games.
A long time ago I made a list of aspects needed to make an interesting game. Magic as important as it is made my list at #8, but clearly effects the flavor of the entire list. Under magic I made a list of Key words that can or should define magic:
Scarcity: Is magic common in your game ?
Do you have magic schools in your game with teachers & desks ? 
Or is it something rare or lost ?
Mystery: Yes magic should be mysterious, unclear, magical you might say. Or is it as clear & common as matches in your game ? If it's the latter, it's not magic, just a technological replacement. You can do that if you want, but magic has another role to fill.
POWER: Oh yes. Cantrips are cute, but why have them when you have a bow & arrow to fill that spot. Magic is something to be feared.
Cost: Does a spell cost a bit of invisible mana or do you have to sell your soul for your trick ? In most games magic has little down side. Mana really is a gun clip in a way. Use it then loose it. Drink a potion to reload. Magic can have a greater cost. I'm not talking about reduced fighting stats for mage classes. Those are just an excuse to allow magic with only the cost to the skill that player never uses anyway. Are you sure you want to unleash the awsome "power" of the unknown ?
Seduction: Only a mad man would use such a thing. Even with that said, the temptation of magic spells or items can make the desperate take chances or ignore warnings.
The one true ring really isn't all that bad after all. They just say it's bad because they don't want you to have it.
Ok, might as well make it a poll:
How important is magic ?
[EDIT] This isn't just a rant. Make your own list people.