Here are some of my insights into the basics of Mage gameplay. First some points about playing a mage.

Pros:
You kill shit quickly
You get to be useful and diverse
Less gear dependent
smaller repair bills

Cons:
You die easily
You draw attention to yourself easily and then die
Easy to replace in a group

First the Pros:
You kill shit quickly: As my friend once said "The only tank I need is the distance between the mob and myself". Most mages learn to kill something before it gets to them. A mage with points in the frost tree will be safer at this whereas a fire mage will be faster. Arcane doesn't come into its damage until later game when you can stack good amounts of INT and spell dmg.

You get to be useful and diverse: As a mage you are endowed with abilities like making food and water, you can make portals to capital cities, you can sheep many targets, and you can spell steel just to name a few. Those abilities are common to every mage. Some mages specced in forst or arcane get a hand full of other fun toys. Yes mages are heavy hitters and are expected to deal 25-33% of the damage in a dungeon, but this doesn't mean you aren't called on to help solve some technical problems also. A mage who thinks their only role is to do dps is missing 4/5ths of the mage gameplay.

Less gear dependent: I will admit as well as any player at lvl 70 that, without my gear, i am prety useless. But even so I would be more useful than a warrior, or a druid, or a shaman. You could level a mage entirely without gear. It would be a bit difficult and take a while but you could do it. Not so with 1/2 the other classes.

Smaller repair bills: Your wear cloth armor, which again means are easier to kill both in dungeons and in pvp but on the plus side cloth is cheaper to repair. You would have to die 9-11 times in a dungeon to make your repair bill as much as a warriors first death.

Cons:
You die easily: And by easily i mean REALLY easy. You have little health and cloth armor. BUT there is a great way around this problem. You can Ice block to avoid attention, you can frost nova, you can blink, you can go invisible to name a few methods for keeping your ass alive. If you pull a boss or elete mobs off of the tank in a heroic or raid, you will die. But if you do it elsewhere you can run around like a chicken with its head cut off and still survive.

You draw attention to yourself easily and then die: You are a heavy hitting class. You deal a lot of damage and likewise are popular amongst your enemies. There are 3 games to play as a mage. 1) deal as much damage as you can while conserving your mana. 2) deal a lot of damage but not enough to draw more attention than the tank. 3) use your key abilities for key moments to guarantee that your party stays alive.

You are easy to replace: Your most common contribution is damage and sheeping. Both of which can be performed by a hunter or a rogue (at least a bit). You are nice to have along becuase of all the neat tricks you can do that no one else can AND you do ranged damage which makes the healers job eaiser to do.

If you want to play a mage well (at LEAST well if not really well) then remember you are more than a glass cannon.