God, what a terrific idea! I wish I thought of it first, I was kind of thinking of making a level with multiple environments and a hub... could've made a surreal subway!
Anyway, congratulations on completing your first level! I enjoyed the concept, but you should really work on your environments. There are many wonderful tilesets available to make much more realistic parks, subway stations, etc.
A couple of technical tips: (a) definitely make use of sounds. Just a little bit of tunnel wind sort of sound (atmosphere 4, for instance) in the subway, a little wind in the park, (b) definitely try to avoid resorting to invisible walls and such to block the player's progress - instead, work with your tileset and produce things blocking the path. Finally, (c) objects enliven the level. You could give the player the eye from the beginning, for instance, and put a ghost or two in one of the stations. A bird or an insect in the park. And so on.
upd: Also, you do realize some of the signs you put into the level are unreachable? Like the ones about the snow blocks and the tall radio mast
. You only get the run powerup, so those are not possible to get to.