Hi Sin,
glad you enjoyed the demo. I hope the full game lives up to your expectations. Sickness is pretty long and eventful, so it branches out a lot more after the demo.
Sickness is actually on sale on Steam at the moment (35% off), and will be on sale again in a couple of months (50% off) both here and on Steam when the next update is released. There's no clear ETA for the next update, however, so I can't be more specific on the timeframe.