I would probably say too much dead space to the right. Takes a lot of the focus off of the tree.

Edit: With what Sean is saying about IS.... forget about submitting a Raster to them. IS does not like rasters.

Thanks for all your feedback so far!

To address some comments
the reason for the whiteish border was just a design to go with the winter theme. It's no problem to take it out, I just thought it looked allright.
I guess I should have called this 'raster' instead of cg... to me cg stands for computer graphics, and is a pretty general term. It was not done in photoshop or any other such program, so I didn't even think that they could be interpreted as PS brushes, very interesting!

I could move the tree more to the right, no problem, I had left that much text on the right for text, etc. I thought of that too when I got the rejection, though I'm certainly not sure.

So on to the more worrisome issue: that istock doesn't like rasters or that this would have been good for IS some time ago but not now: so, if I say follow all the advice (move tree, take out vignetting, improve shape of tree, and maybe whatever other people have to say), is it still likely not to get in?

Thank you very much for your time, and have a good weekend!
-adijr

...and a couple of weeks later i caught some time to work on this. I tried to improve the image overall while taking into account what you all said. It's pretty much a different image now... Does this have a chance at getting in?

http://depo.fotozygous.com/stock/gct_wm.jpg

Thank you for all your feedback again,

adijr