Because it casts a whole bunch of spells for free at the beginning of your Storm turn, because almost all of the effects are Suspendable on turn one, and lastly, because almost all of the effects are either--you guessed it--draw or ramp
Astral Dragon is a pricey card these days, as is Artificer Class, while Firkraag, Cunning Instigator (the decks Commander), will set you back $10, too
Now that we have deserts that ping, this card can be a very dicey card to cast, as the next land drop from your opponent might be fatal
This thing will basically always give you an immediate impact that is powerful and then if it sticks around the game is well and truly over for your opponent 5/5 worth of stats for 4 mana is a great starting point, and the Gutter-Dweller also happens to be able to grow and draw you cards using the expendable bodies he gives you