While, in general, you have a pretty nice looking sprite there, for the fire bird, a couple of issues are standing out to me a little. The main one being the varied directions of it's wing and tail flames. Flames usually flicker in a certain direction, either reacting to the wind, or simply flicking upwards in the absence of any other outside forces. As it is right now, it just looks somewhat rough and zig-zag-y. It also doesn't make much sense for there to be any shadowing on the one side of the twist above the tail. The fire is making it's own light, so it won't be affected by normal shadowing rules.
The composition of it's design, however, is nice. I really like how it's body is formed.
@ganonfrog: Thanks for the constructive comments. I'll keep that in mind for future works. Afterall it was my first time drawing a fire enemy of such size so you can expect some inconsistencies here and there. I might make adjustments on a later version but I ain't much concerned with making this game perfect (if I were I would never have submitted it). I'm glad everyone likes something about it though ^^