Has anyone killed this thing with a weapon? If so, what did you use? I've tried everything I have with restore health potions to boot and it wins everytime. I'm only level 9, is this the problem?

All you need is an enchanted weapon.
Daedric and Silver will do too.

Enchanted, Daedric, Silver or Spells works

i like trying to shoot disappearing enemies with arrows, makes it challenging. with a decent close range weapon and doing hit and run attacks, it can become easier. however, i've found spells work best, as it lets you keep your distance.

I just kept moving around in circles. The attack of the wisp is on touch and they show themselves before they engage the attack so you can get out of the way hit them a couple of times and jump out of range again.

You'll need fairly highspeed for this though.