It is adjustable, so it may be good or bad depending on your preferences.
For me, I turned it off. Solid 60fps was more important for me.
I think in terms of still image quality, it looks worse than having it off, even with high AA settings. As a regular screenshotter, this bothered me, and especially because you spend a lot of time seeing closeups of Geralt where it was most noticeable. Non-Hairworks hair looked better when still.
To make Hairworks not destroy your performance by up to 30-40%, you had to turn down quality level and AA. While Hairworks in its prime form looks fantastic in motion, its a shimmery mess at lower settings. As somebody who is sensitive to aliasing, this bothered me a lot.
My ultimate conclusion, for me personally of course, was that I could deal without Hairworks on Geralt completely and only have it for monsters. The big hunt monsters looked spectacular with Hairworks. But lowering the settings ruined a lot of this.
I could never really find a balance where I found it was worth it. Then again, I run a GTX970. If you had a 980 or especially a 980Ti, I'd probably have made the sacrifice and still been able to hit 60fps. At 1080p, at least....