When the Hunter changes dropped earlier this week, I understood the Volley change, and I even got the Kill Shot cooldown drop, but the one I really didn't understand was the Deterrence change. Like BRK said, it seemed pretty useless: sure, becoming immune to damage for five seconds helps survivability in the Arenas, but what's to stop people from just continuing the kill after that. And the directional effect was just perplexing as well.
Now, Ghostcrawler has provided some background on the change, and while it still doesn't make much sense, at least we have an idea of where Blizzard is coming from. First things last, the directional ability is still being tested and may not make it to the live game. But the ability itself is designed specifically for Arena, as we'd guessed. And even more strangely, he says the reason they wanted to change the spell was to make it different visually -- letting the Hunter see themselves parrying every single attack while their backup helps them out. That argument may not find much ground in the numbers-driven Arena crowd, but GC says lots of times, a strong visual can give what seems like a useless spell a lot of use. Interesting look into Blizzard's design philosophy -- they don't program the numbers, they program how it plays.
Finally, he says that Hunter melee damage is being looked at -- they are primarily a ranged class, but the problem now is that it's all or nothing. Either you're in a Hunter's barrage or you've closed to melee and they're not a threat. If they can put the sting back in melee, GC says (within a few patches -- this is long term), then they'll give them more viability "to flee or stand and fight." We'll have to see what Hunter's think about that one when we get more specifics.