There's something about the twisting nature of the Tree, that reminds me a bit of the Whomping Willow from Harry Potter. ^_^ That's by no means a bad thing, it gives the tree a sense of active personality. It's not just stagnatly there, but it has a character of its own.
The sort of mountainous terrain reminds me a bit of a Chinese ink brush landscape painting.
I also like how you made each of the Norns different, and how you settled them into the composition. I love that sense of scale of them versus the "WORLD TREE" . They may be Goddesses, but the World Tree ties the 9 Worlds together, and is truly, massive. So while I think some would focus more on the human seeming Goddesses as the 'focus' of the piece, I actually really appreciate how the tree is the first thing you notice and see.
The one thing that felt a little odd to me was that you had these bold graphic lines around the Tree, and the rocks and mountains, but the Norns themselves almost disappear into the rest of the piece. It seems like they might benefit from something that would help them be better differentiated from the rest of the scenery around them. There's a sense of light and shadow around the roots of the Tree and rocks, and even a since of shadow and depth among some of their clothing, but not among the Norns in relation to the scenery (grass, etc.) around them. As it stands now (and perhaps this was your intent) the Norns are absolutely the last thing I see. I see the well before them, the rocks, the trees.