I'm liking the new Arena format.
Increased chance of high raraty cards make the games much more varied.
I just managed to combo Majordomo deathrattle > heropower = 8 random damage.
+ a discovered Coldarra Drake (Use hero power as many time as you want.)
I think the increased frequency of spells absolutely sucks.
I lost as a Paladin at 2-2 to a mage with:
3 Blizzards
2 Fireballs
1 Flame Lance
2 Polymorphs
2 Flamestrikes
within his first 21 cards, as well as a whole bunch of other crap. (including two of the random-potion guys, which gave him a Felfire potion (just when he needed it) and a greater healing potion when he was down to 4hp).
Everything I played got immediately removed. I never even drew my Tirion (ever in the whole run, in fact).
When I finally got one thing down that looked like it would stick (I had quite a few lategame minions), I had 10hp left and he had 8. He topdecked a pyroblast.
So yeah. Who knows if that's a typical experience against arena mage now. But I really hope it isn't.