Izzet colours! Tempo! Control! Draw cards! Scry! Bounce! Burn! Counter! Sphinx it! (yeah I know AEtherling is better but it's a really expensive card right now).
Key Spells:
Anger of the Gods makes this whole deck possible. Throws an opponent's aggro in the bin for a relatively tiny mana investment. Board in some Cyclonic Rift and/or Mizzmium Mortars against midrage or bigstuff decks and you're laughing.
Thassa, God of the Sea and her Bident of Thassa is an extremely appealing scry/draw engine.
Turn / Burn will remove anything, even a god.
Magma Jet and Izzet Charm will do some serious work in this deck.
Steam Augury for card advantage and, at worst, a bunch of Spellheart fuel.
Creatures:
Frostburn Weird
is a 2 mana U/R hybrid that survives Anger of the Gods and enables Thassa with 2 copies in play. The Anger/Frostburn package is the cornerstone of the deck.
Prognostic Sphinx
is hilarious, has evasion, a big butt, can be protected in exchange for Spellheart fuel, and will scry so deep you'll never get an unwanted draw once it's in play and attacking.
Spellheart Chimera is an interesting one. I see a lot of people brewing it for Izzet Blitz (and I've had a go at this myself) but its true power comes much later in the game and it simply can't replace the Nivix Cyclops as the centrepiece of a blitz deck. In this deck you'll be throwing enough instants and sorceries around in the early to mid game that the SC will have plenty of fuel by the time you're using it.