I like your ghost house gimmicks. You might consider putting the poison water in Walnut Secret down half a tile or something, though, since the platforms that are on the bottom tile of the screen are difficult to see when they're almost completely submerged.
While the Idea sounds nice in theory it doesnt look like you did a lot with it besides palette and small enemy/layout changes (The berries probably coming nearest to a nice idea). The four seasons bring a lot of ideas with them that can be used very good in a level.
And while I was watching the video I was more confused then anything most of the time and I didn't really know what was going on at the moment or where the player was. But that might differ from when I am playing the level on my own.
I have to agree with Tob here; the idea of the level is cool (I was always a sucker for season switching gimmicks) but unfortunately the level didn't really seem to use the seasons to its advantage. I really like the idea of the falling berries in the autumn, but the seasons didn't do anything else, other than changing the layout of the level.
Maybe you could hide a Dragon Coin in a horizontal pipe above water, than can only be entered when it is frozen over in the winter; it would make the seasons at least feel more involved with the level, instead of the Dragon Coins being hidden in a kind-of door maze.
-------------------- I don't even know what I'm actually doing anymore... will I ever finish a hack?