In 0.6.0 they changed the melee damages a lot. It now takes 3-4 hits to kill someone regardless of where you hit them. Please vote in the poll and make your opinion on this known!
Personally, I'd like to see two hit melee kills everywhere except the back. Melee hits to the back should be one hit kills, but they should perform various "execution" animations similar to Battlefield 3/Halo 3 (and newer). Take a look at the Assassins Creed games for execution animation ideas, they can range from simple unarmed attacks to things that involve knives or surrounding environmental objects.