The piano at the start is too bright for the rest of the ensemble. It's clashing in feel with the rest of the ensemble- consider a softer/lower dynamic. If you have a close-mic'd piano, try that.
This kinda makes me think of fall actually. A touch of melancholy, but still upbeat. Winter is much colder, more open. This has a great deal of warm mids, like autumn reds and oranges. If I were doing winter, it would be more ambient in nature and with few 3rds in chords- implying openness and emptiness, like winter. Emptiness =/= simplicity necessarily. Something can be empty but not simple.
Of course, one might say it all depends on how you look at winter... Maybe winter is a time of joy for you. However, the final determination is in the picture. Notice the cold blue tones, the rich purples, the way the nymph/niad is frozen in her pond. It's dark, mysterious, lonely. Not exactly time for hot chocolate and candy canes.
I really like the vibe of this piece, but it just doesn't quite fit the image I am seeing. Good composition as well, nice variation, nice motion, etc. Only the beginning really needs some tuning up. Think about how one would frame the image you chose. Is it surrounded by snow-filled clouds and snowflakes fluttering down? The beginning of your piece is the frame to the image- the establishing shot, if you will, telling us "this is winter, so I hope you brought a frelling coat!"
Total: 62/100 (NG: 3 stars)