Left side is too empty IMO, but I don't know what to suggest for it to be filled. Interesting concept, but it would look better if it actually had a background.
You must have a shitty/old monitor because there is a background. I'm not even going to respond to your too empty comment because sometimes a piece NEEDS to be empty to have the effect it's supposed to.
I really like the feel of this piece... it has a great light-dark contrast, and I think it has just the right amount of content, given the title/meaning of the sig. The effect you have on the silhouette of the person is very nice, and the slight hint of color that it adds works very well. My one complaint is the way that the text warps with the smoke. Did you use the displace filter? If so, you could probably increase the effect by 15-20% to make it more dramatic... If not, then the displace filter would work very nicely here, at, say, 30-40%? Its just a suggestion, but I really like the sig and I think that the text doesn't do the design justice.