If there is one thing that looks out of place about the cover system it is that it has a very Eldar look to it, obviously being that it appears as a bubble shield. Now when there are Eldar sitting inside this cover (per below) it looks 100% fine, it makes perfect sense in the landscape.
The issue I have is that there is a bit of a missed opportunity when it comes to Orks and Space Marines. I think the appearance of the cover should customize its appearance to the race that captures it. For example:
1. Eldar captured cover - bubble shield in its current form used to protect circle
2. Ork captured cover - scrap pieces of metal/materials starts being pulled together in a circle
3. Space Marine captured cover - sand bags and tank traps are mixed together in a circle
I think this individuality gives the game more clarity and would be much more visually appearing. Instead of looking at the cover system as a shield bubble you can capture we can look at it as zones that are optimal to construct a cover system. The construction would obviously happen as you gradually capture the cover with your units.
Wish I had thought of this a few months ago instead of now...