Ooh, shiny. Wait, what?
Are you going to put the circular icons in radial menus like Dreamfall or are they going to be in bars like WoW (and your previous screenshot)? I'm feel kinda dubious about the idea of round icons in bars, but Civilization 3 got away with it, and it didn't bug me (though the game did). Thing is, UI (I hear) is better if squared buttons are set against a side of the screen so that the user can run their mouse against the side of the screen to get to the button because that's much easier than centering on a square floating in space somewhere.

Then again, you seem to be developing the game in windowed mode (as am I), which kinda negates the advantage in that. The Dreamfall radial menu on-demand is a cool idea which might be more immersive (and certainly works with circular buttons). I think Planescape: Torment had a right-click radial menu too, though I don't recall using it too much. Neverwinter Nights 1 and 2 had radial menus too, now that I think about it, but I never liked 'em for some reason. Maybe you could have the option of either? Well, whatever actually works is most important, in the end.
Ok, done rambling!

I knew someone would call me on my flip-flopping! Nevertheless, the final icons, which I haven't shown, combine the wood-and-metal look of the first with the clean roundness of the second.

Good points about useability. Currently, I don't account for transparency when checking for mouse-click intersections with any user interface elements. So the icons are always square with regards to interaction.

I'm not doing any radial menu stuff, although EDI was using that for one of his games a year ago or so. And its not a no-mouse-interface a la Dreamfall either. Essentially there's going to be a command bar at the bottom of the screen with four icons at the left with a text-entry box filling up the remaining space.