When you can make your car look more dominant then it is, you are putting together one hell of a performance. For that, Schumacher 2004 and Vettel 2011.
While the 1993 McLaren was not as bad as some make it out to be, Ayrton Senna most definitely had an inspiring season. 30 years before, Jim Clark's 1963 championship season was one for the history books as well
Alberto Ascari's 1952 campaign was truly one for the history books, winning every race he started, but the Indy 500.
Almost but not quite
In 2012, Vettel, Alonso and Hamilton all three had very impressive performances, each having their own guardian angels to protect them and their own demons to fight, but they also each made their mistakes and I feel their over-all performance would not fit into the first category.
In 1998 and 2000, Mika and Michael put together fantastic campaigns, but I feel they did not quite fit in the above slot.