It doesn't have any functional changes or improvements over the 2.0 version. So why the big release? Configuration baby, configuration.
Debian's resolvconf has plenty of mini configuration files, which openresolv has supported. This is quite problematic from a package distribution and maintainability perspective. Also, the implementation required plenty of forking sed or equivalent to parse them which is inefficient.
So openresolv now sports a shiny configuration file, which I think is more flexible and easier to manage. It has a downside and an upside. The downside is that you now have to configure the files to write resolver configuration to for dnsmasq/named. The upside is that if they are unconfigured (the default) then the subscribers don't litter /etc with files you'll never use.
Also, the subscribers themselves have been moved out of /etc and into /libexec as they aren't really configuration files.