Instead of it slowing down
for everyone, why not make it so it only slows down
for you? I mean, of course things would have to be adjusted so you would be able to like do several neat tricks and be able to dodge bullets (matrix style

), also, since you are in slow-motion sort of mode, maybe you could see other players moving slower then they really are, to give it more of an effect. Now, the person in slow motion mode will have to be given some sort of special effects so that they couldnt be owned easily...sort of like a good way of dodging bullets coming towards them, but it cant be impossible.
Not sure if you guys understood what I meant, but if you did, then great.