This is how Hearthstone looks on a Nexus 7 (7 inches tablet).
If you have followed the news when Hearthstone was announced, you might have heard that the game will be launched at some point for Ipads. The game wasn’t announced for Android yet.
For 7 inches tablets, the main problem is with the resolution. The cards and how the main UI looks, you can barely see anything if you don’t keep your tablet at 5-10 cm from your eyes.
What Blizzard could do is to increase the size of the cards and reduce the environment elements (those four buildings from the corners).
However, I think that the game is playable on a 10 inches tablet even as it is now.