I have a pretty beefy computer (32 gig ram, 24 gig video, 3.4 GHz proc) so I tossed it at max graphics "Mythic" and was working fine. However, I just tried setting it to lowest graphics "common" to see what the difference was... and suddenly everything lagged. Longer to start battles, slower animations, less responsive to click (having to click the cast button twice). Pumped it back to "Ultra-Rare" and everything is smooth as silk.
Not sure what is up with "common" graphic level, but you might want to avoid it.