Art style is absolutely great, except for one thing
Hero, unit and map art style is astonishing. I totally love the smooth and clear, but not childish graphics. Units are lovely: cute, simple and elegant. Great job on that!
However, what's up with the action icons, the ones in the UI that represent abilities and production? First thing I thought is that they are placeholder icons straight from Google Images. I hope I'm right and the criticism that follows is unwarranted. Note that the following doesn't apply to Unit icons, as those are meant to closely depict the unit, and already look good enough.
Major problem is that most icons are too detailed for what an icon should be, i.e., iconic. The Resource tab icons are what icons should look like.
For instance, Attack and Stop are "signs" in 3D with a shadow projected into the "floor" instead of the background, and slightly turned around. Icons shouldn't try to fake 3D. Embrace the 2D of the UI and make icons iconic: simple and clear, much like traffic signs or bathroom signs.
The ugliest icons are the general upgrades: Ability Power, Attack Damage, Magic Resists and Physical Resist. I'm assuming they are totally MS Paint placeholders, and are going to change, so no comments on them.
The ability and per unit upgrade icons aren't as bad, but they have a way too complex color palette and lack stylistic consistency.
Comments
You're completely right. The action/ability icons you're seeing are placeholder. Unfortunately we weren't able to give them a coat of paint before the open alpha started, but they should be updated soon!