I think this is a really nice shot. There is excelent detail in the feathers which I really like to see. I personally would crop off a little more on the right side. For me though while I like the photo and I think it is technically sound I prefer photos that show the whole bird when photographing small song birds. I am impressed though that you were able to get that close. I have many shots of cardinals and I have never ben able to get that close to one.