This guy has put together what he thinks is a top 10 list of the best treehouse of horror episodes. He hits the nail on the head with one point:

Now you may notice that all of the selections are from Seasons 2-9, but lets face it, Season 9 was the last time The Simpsons was any good anyway…

But I don’t agree with his list. What about the one where Homer goes 3D? Check out the list.