This already looks like it's going to be a good map!
1. I think that the circular play is fine; making North/South or East/West attack routes will make it a bit too complicated.
2. The first thing I noticed was the three pink bits that didn't seem to have borders. I know you've spotted it, but it just leapt at me.
3. I really like the texture in the background, although there may be others who find it a little distracting... not too sure what to suggest - perhaps altering the blend options somehow?
4. The snowy area on Dalvik (green) has a solid outline, which it doesn't on the yellow or pink areas. Can this blending be made to look slightly smoother?
5. I think you said you're still playing with colours. At the moment I think the green/cream are too similar.
6. I think the territory borders are a fraction too light, and could be darkened ever so slightly.
7. On the first draft there was something that looked like it could be a territory on the coast between Skeidarar[...] and Hofn. I didn't see the sea route there at first (because my eyes don't work properly
), but you could consider putting that in as an additional territory. I'm not recommending this by any means, but it might help give a 'complete' appearance to things.
These are just my initial thoughts - but I really like the look of this, and am looking forward to seeing it develop. As others said, it looks like more than an idea already!