- Too much emphasis on Arenas and not enough on Battlegrounds.
- Too much emphasis on 2s and not enough on 3s and 5s.
- Not enough class / spec representation in Arena. Warlock, hunter and shaman numbers in particular are too low, but they're not the only ones.
- Too fast-paced.
The charge that burst damage is too high is also old and not entirely accurate. Blizzard points to the fact that healers are also powerful in Arenas -- borderline overpowered, actually. Very few Arena teams find success without a healer. Ghostcrawler reminds players that healers are so important that not having a Mortal Strike-type debuff "may be a huge liability." It's a delicate problem, and Blizzard is afraid that nerfing burst damage across the board can lead to extended matches where crowd control remains the only solution.
Speaking of crowd control, some players pined about the dominance of Rogue / Mage / Priest in Arenas. The viability of the comp is undeniable as it continues to win tournaments through different seasons. Blizzard agrees, noting that they'd "prefer to see other comps as dominant as RMPs in 3s," but explains nerfing the comp would probably simply lead to the dominance of cleave or double melee.
He brings up an old point about Resilience gear not being readily available at the beginning of Wrath of the Lich King or sacrificing too many stats to the point where it was more attractive to use PvE gear. This contributed to the perception that burst damage was too high -- the damage output has generally remained the same but more players are sporting resilience now, allowing for slightly longer, more strategic matches.
As much as Blizzard points to the low representation of Warlocks, Hunters, and Shamans this season, it should be interesting to note that these have fluctuated over time. In particular, Blizzard managed to raise Hunter representation in Season 5 to the point where Survival Hunters needed to be nerfed. Warlocks also enjoyed decent representation in earlier seasons, so it's a continuous challenge to balance the classes. Shamans, unfortunately, have yet to enjoy their time in the limelight.
Ghostcrawler also stresses that Arenas aren't going to disappear (sorry, guys). He explains that some people actually enjoy Arenas "because they are quick, easy to organize (relative to a Battleground), often have fast queues, and / or they just enjoy the 'purity'" of a death match without the burden of map objectives. Blizzard understands, however, that players who don't like Arenas are forced to play it in order to acquire the best PvP gear and would like to fix that. The key issue with this is that Blizzard needs "to develop a way to reward good gear through BGs that isn't based on endless grinding."
Whether we'll see that solution as soon as Patch 3.2 remains to be seen. Blizzard is definitely looking at some interesting things for PvP and the Battlegrounds, and part of that is a means for Battlegrounds to be as rewarding as Arenas. With Blizzard relatively quick to respond to player issues, hopes are good for positive changes to WoW PvP... soon®.