I put on my wizard's hat and robe!

I'm just going to link to Gatherer because I don't feel compelled to link everything.

If anyone plays Magic with me they know my favourite colour is blue. What is the defining feature of blue? Card draw. If you have more cards, you have more options than your opponent. If you have have more answers than they have questions or more questions than they have answers, you win.

This is why aggro decks like Red Deck Wins wants to run a tight mana curve, by minimizing the amount of land they're running, they draw less land on later turns and more threats.

Some green decks tend to have larger creatures, they maintain the same advantage because much of their mana accel (e.g. Kodama's Reach) doubles as deck "thinners". By removing land from their library, they are increasing their chances of drawing more active cards later in the game. By the same token that's why the fetchlands are good, sometimes even in a monocoloured deck. Also why Land Tax is banned.

Control decks run a higher land count, but use card draw to gain advantage. Instant card draw is significantly more powerful because it means the blue player can leave lands untapped for a counter while being able to use their mana if nothing gets played. In a true Draw-Go deck, the entire purpose was to build up an overwhelming number of cards, more than enough to handle all threats, then win with something small and ridiculous. Like Rainbow Efreet. One copy of it. But WotC decided that was too good for blue so they're refraining from printing any more*.

Combo decks are ridiculous; I don't want to talk about it.

That's why cards that let you draw 1 (e.g. Serum Visions) are extremely cheap, because you have no net gain in cards. But as soon as you increase to draw 2 cards, the fair price spikes to 4 (e.g. Inspiration). Of course Ancestral Recall was not fairly priced, and as a result it is arguably the most powerful card in the entire game (along with Black Lotus and Yawgmoth's Will...Time Walk wouldn't be very far behind though).

But card advantage doesn't stop there, it encompasses everything in the game. If you play Mystic Snake, you've answered a threat while delivering your own, another net gain of 1. That's partially how Shriekmaw became the best card in Lorwyn limited and its forefather Nekrataal was a power card in its heyday. If you play a Wrath of God and destroy 4 opposing creatures, you've answered 4 threats with only 1 card. That's a net gain of 3!

To extend it further, that's why Leyline of Lifeforce is stupid answer to control (barring specific metagames). If you play it late, it does nothing. If you draw two of it, it does nothing. If you're not facing a counterspell deck, you have wasted slots in your deck for a card that does nothing. Compare that to Vexing Shusher, at worst you've still got a 2/2 for 2 that's pressuring your opponent and at best you have both a question and multiple answers in the same card. Card advantage.

On a wholly different note: why Plague Wind is terrible. If you're losing, you can't retaliate until at least turn 9. At that point, any self-respecting aggro deck would have you so close to death that any burn spell, any random 2/2 that gets through would kill you. If you're winning, well you clearly don't need Plague Wind then. Damnation would be a better card 90% of the time, closer to 100% in a tourney caliber deck.

I actually dislike playing affinity as much as people dislike playing against it. There's not a lot of subtlety involved. My favourite deck is now the Izzet one. It's decent enough for casual, flavourful and Gelectrodes are fantastic. It would also be good for Emperor because it has repeatable damage, Cursed Scroll style.

On the other hand, I can't lose with Islandhome, if I don't win it's not a real loss because nobody really expects an Islandhome deck to win and if I win then I beat the odds.

One thing I can't understand is how people manage to play aggro decks wrong. It's not difficult, you always try to be attacking. It doesn't matter if it's a 1/1 Llanowar Elf, if there are no blockers, swing with it. The longer you wait, the longer a control player has to draw an answer. If they already have an answer, well tough luck; holding back isn't going to solve anything. If you get a control player down to a low life total, it means they've lost options because they can't afford to let any damage go through. It means you have the initiative and they're forced to spend their mana and cards immediately instead of investing for later. That's why River Boa was such a power card against Draw-Go decks, because it immediately put the other player on a 10 turn clock.

edit: Colour me unimpressed by Thomas' boasts about spending $35 at Image. I don't think he realizes that the solution to burn (and pretty much all forms of control other than counterspells) is Troll Ascetic, not more Vigors. I also relish the fact that the Izzet deck cost me ~$10 to make and affinity costed ~$7.

*At the same time, the top-tiered deck in Standard is faeries? What the hell, since when did blue have such efficient beatdown? Back when Fish was actually a merfolk deck...AKA before they stopped printing merfolk. In conclusion, Guilty Gear > Virtua Fighter.