I think I've done seven critiques since joining DeviantArt, so here come an eighth! The first thing for me to say I'm impressed! Though I personally don't know a lot Jack Frost nor Critiquing.
His staff is very vibrant, and the glossiness you added helps with the luminescence in this whole picture. All the shading you put looks to be in the right places. It's really well done in my opinion, but critique wants you to state what ya like and don't like. Don't like the second part of that sentence.
This isn't really what I don't like, just tips. His mouth looks a little too long, but that could be your style, so no real worries. The only thing I don't really like is the hand up front. It's proportions are right, but it doesn't look like there is enough detail. I'd recommend you add where his finger nail would be. But that's about it of what I think is wrong, in my opinion.
VISION Your overall vision is nice and really good, so goodness there.
ORIGINALITY If I haven't seen the pose before, I think it's 100% original, and the pic does have it's uniqueness to it.
TECHNIQUE The technique is nice, but could use some fine tuning, but other than that, really good!
IMPACT It's impact to me is good, but not OMG. So I'd have to give it a standard. I'm definitely adding it to faves, btw! Hope I didn't sound rude, I'm really not trying to, I'm still new to critiquing.
(This is my second critique, my first one done this morning.) ^.^
Firstly I'd like to say, the moment I saw this, (being the huge Jack Frost fangirl I am) squealed like a.....well.....an elated Jack Frost fangirl. I can't say this is the BEST Jack Frost fanart I've seen, (I've seen lots) but it is certainly up there. I think the colors are the best, the expression especially gets me (THOSE EYES!!), and you did a great job with the lighting, I love how the only source is his staff. It's good how it's dark but not too dark, and even though it IS dark it's still got a happy/float-y/magical feel to it.
The leg in the back kinda confused me a bit. It almost looks as though the knee is on the wrong side? I feel like the way the thigh is positioned, we should be seeing the SIDE, or maybe front of his foot and not the back. That may be just me, I don't know. At second glance, the lining on the staff seems a bit weird, kinda like it needs to be sharper, but that also might just me.'
Overall, I am impressed, and looking through your gallery I feel as though this may be one of the best, if not, the best piece from it. Keep up the good work!