I used to think that a mill-deck was the pinnacle of irritation, around when Zendikar came out and a buddy of mine made a blue/black mill that got me every time. Tonight, I played a deck that revolved around cards that were so strong that one of the conditions was that you would lose the game at the end of the turn, and he had multiple ways to prevent the turn from ending in that way (via the spell-stack) or negating his ability to lose the game; the win-condition was that I was given a card that had four abilities to be chosen one at a time (the last of which was "you lose the game") through a "target player takes control of target permanent" card. The remainder of the deck was different variations of the "Fog" card; I.E., all damage is prevented during this turn. This was combined with cycling, cards that allowed him to have various "hands" worth of cards on a stack to be cast at any time, and so on. That is basically what I'm talking about; it was absolutely clever and absolutely effective, but didn't really represent what I felt like the heart of MTG represented, and that is absolutely a personal perspective.