Pros:

Great map!

Cons:

Can't install the new version.

Conclusion:

I have played this in the past and its awesome.  I saw there was a new version so I decided to download it but when I open the zip file I keep getting this message:  'helms_dr20.vpk' is not a valid Source engine add-on.  Installation failed.  Any idea of what is going on and how I can fix it?  I have tried several times to download it and keep getting the same message.