Hey Bungie! People have probably already brought these to your attention, but I thought I'd list a few issues I've had over the past few months in PvP...
1) Hunter's Flux Grenade: A lot of times it will hit a target, and then simply bounce off them, seemingly for no reason; it also curves to hit enemies at times, but at others it will fly past them by one pixel - or just phase straight through them! This happens more often than not.
2) Warlock's Axion Bolt: I have seen this mentioned before, but at times when I launch the grenade, it just disperses in a poof of purple smoke, no damage, no nothing.
3) Blink: Needs tweaking. An enemy shouldn't be able to kill you with a hit AFTER you've Blinked; what are they shooting, stray light particles? :/
4) Radar: When someone is behind a wall, or a pretty good distance from me, the radar will flash in the middle, indicating the target is right on top of me. The middle of the radar should only flash if they are within melee range, and even if they're close, if they are behind a wall, the radar shouldn't say they're right on top of you, it' misleading.
There they are, the big four for me. Hope you can sort them out ^_^