Ryzen is a strong competitor. I would say that unless you're doing 120-144hz gaming (in which case go for an i7), the Ryzen 1600 is a better value chip for most tasks than any Kaby Lake i3, i5 or i7. Ryzen 3 hasn't been released yet, so those looking to purchase a basic web browsing machine will probably be best served by the $60 Kaby Lake Pentium G4560.
As for what you're coming from, that really depends on your needs. For some people looking to get those last couple of frames per second, even coming from a Haswell or Broadwell i7 can make sense. For others who need the decoding and output improvements in Kaby Lake's iGPU, it can make sense. There are others who are still using an old Core2 CPU which serves their needs nicely, and...