I ain't spending the dosh for Legacy, and all the decks are already found there, or most of the serious ones at any rate. Modern has room to fiddle, but the arbitrary, turn-4 ban list and huge prevalence of Abrupt Decay and tempo-base disruption (read: Twin's blue) put harsh checks on the format (though Enduring Ideal/Zur looks promising). Standard is god damn mosh pit. In Pox, you can do whatever crazy crap you want, because there's always the chance you get outplayed on the field. (I still love MtG, but Pox is more fun.)
Chess-ness. ALSO, could you finally patch out randomness, it still pisses me off to an unreasonable extent.
My favorite MtG deck consisted of Verdant Force, Altar of Dementia, Coat of Arms, and a bunch of ways to get more lands out or mana generation. There was other stuff too, but that was just filler to survive until I had the Verdant Force Altar of Dementia going.