EDIT: On a balancing note, your changelog doesn't mention any changes to Aard's stun chance? Aard with the stun upgrade seems also a bit too powerful, but perhaps that's just me. I guess if it's intended to work reliably on lower ranked enemies (harpies, nekkers, basic swordsmen), that's fine... still, I stun-killed pretty much all of the harpies in the harpy wave in Arena by spamming Aard.
(To Costin)
I second that; there's no way to attack mages directly, currently. You ALWAYS need to cast a sign, which they block with quen (dat reaction time... even if it is that way in vanilla, it's still pretty ridiculous), after which you can start hitting them. If you attack them directly, even with a quick attack, they will quen during your animation and Geralt gets slammed down.
I've never been particularly good at Arena, but just like Costin I found the only way to survive currently is to Aard/Igni, hit once or perhaps twice, and roll (OK, pirouette) away again. Perhaps I'm just doing it wrong, but in that case I'd like to see some video footage of what I should be doing. Maybe if Costin changes his mind after a couple of patches : )
I should add, though, that the changes to Quen and the increased responsiveness are enough to win me over, and I'll definitely be using FCR on my next playthrough.