Great News! Google is now making the NIK filter set free to all. Check it out at https://plus.google.com/+NikCollection/posts/AFGsG2Di7EK
In my opinion, HDR Efex Pro 2 and Silver Efex Pro 2 are the best of their type at any price, and Color Efex Pro 4 is still a cool way to punch up your images. The other filters are worth having, but are not generally first in their class.
Google bought NIK a few years ago and stripped out the engineers to work on mobile projects, so the line is static. But I paid about $600 for the filters over the years, and they are an everyday tool in my workflow. Don’t pass this up!
Best regards —
Jeff Carsten