In my opinion, If a melee is delivered to the back of an enemy, it should be an insta-kill.
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Melee is fine. Instead of melee before shooting, shoot then melee. Works like a charm. Also, there is no possible way to get snuck up on or sneak up on people. Unless they are god awful, you are god awful, or if you are aiming for too long or your opponent aims for too longg. You dont even need to look at the actual game really. All i needed to look at was the radar and i did pretty great in pvp.