Holy hell I haven't been playing this for 3 years, what can I expect as new?
Since 3 years ago, I would say 75- 90% of the content would be new to you. I remake content in every update so playing from the beginning would be a new experience :)
Though in your case, I recommend waiting until v0.17 is done as that will include even more content and remakes of older content.
The main content for v0.17 has been finished, so it will be done soon :)