I was bouncing around in Warzones last night, playing on characters in all the brackets, and was surprised by a few things.
Firstly, it appears (and maybe I am queueing incorrectly) that the new Arena's are a part of the regular unranked Warzone line up. This is surprising for a number a reasons, mostly that it seems a very odd "warzone" to PUG and it seems horribly unfair in the cases of the pre-55 bracket. For instance, my 49 Juggernaut was put in a group of fairly high 40's and low 50's for one of the random Warzone-Arenas, and we faced off against a group of mid-30's. Granted, they had a balanced group and we had 4 DPS, and there was bolster, but still...it just felt wrong.
As for the Arenas themselves, I saw maybe 3 different maps across 4 characters and I do like the format. All of the matches went VERY quick, and do like the 2-out-of-3 format instead of just doing a single match. The Arenas themselves seem well designed and have a lot of tactical options to play with LOS. The only thing I think would be cool to see added are traps and/or pits that could really make for some interesting environmental gameplay.