Quick reply:
#1: I like the composition, although I'd try to get in closer (to see more of the grasses -- they're cool). Also, branches in the top left are distracting, but easily removed.
#2: Nice subject, good composition. The rocks are interesting, and the angle lets the ice recede into the distance. The hilights look a bit blown out.
#3: My favorite. Very geometric, almost abstract. You could use some curves or levels to make the thistle really pop out.
#4: Interesting, but crooked -- should be straightened. The lines of the railroad are nice, but could do more to lead your eye in to the grainery if you changed the angle a bit -- try having them come in from one corner, for example. You might also get lower, to emphasize the rails more.