Ok, nice blue, heavyset guy.
People will criticise you for using "heavy black outlines" - I don't mind this, but that is what you will hear here.
I think your sprite could benefit from changing the skin tone slightly, I mean if you made him a slightly more greyish blue as opposed to the kind of neon blue you've used, you may be able to get some nice texture in. You've put some in, I just don't really see it so clearly. I'm unfamiliar with that aspect of Norse Mythology, so I wouldn't know what a jotunn warrior is meant to look like, but I see a lot of body mass on the top and rather small legs. Ignore this comment if that was intentional.
Finally the axe. It looks like the axe head is at a different angle to the shaft, maybe consider changing the way the weapon looks.
Nice unit, very original, despite what I said about the skin tone, some blue skinned guys would look good in Wesnoth, especially in the snow. Draw more.
...apparenly we can't go with it or something.