This is gorgeous!
The pop of color is stunning, truly. The softly vibrant red is perfect for the muted tones of the background.
I think the focus is perfectly fine. Even though it's not 100% sharp all over, I think it works very well here. The lighting is soft, the colors are soft, and the focus only enhances that softness- but in a complimentary way, not in a "My eyes are going cross from being so out of focus!".
The snow riddled along the railing is nice, as well as the soft flecks on the beak. The closeness of the subject to your eye is well placed, due to the angle the beam in the back adds a nice touch of length to the photo (which is why the placement of the cardinal is so nice here).
The main things that I love about this photo are one- the clarity of the eye. I love pictures where you can see the bird's eye color. It's so clear, in fact, you can see a soft pattern in the eye that makes me love it even more. The second thing I love about the photo is, as stated above, the softness of this picture. It feels like a warm, lovely winter day instead of just a brisk, cold winter day like most bird pictures taken in snow. The last thing I love about this picture is that, despite the placement of the cardinal in the picture, you can still see it's tail (which adds another touch of length to the photo). If I couldn't see the tail of the cardinal, I don't think I'd have liked this picture enough to write this review.
The reason you only get 4 1/2 stars on originality is because there are so many bird in snow pictures. The reason it's a half, not a flat four, is because of the placement of the cardinal, and the softness of the picture (which is different than norm, as stated above).
I applaud you, and your photography. You never cease to capture my eye with your beautiful work.