I'm a former nmap core developer and even though I no longer actively contribute the project still is very close to my heart. It wasn't "revolutionary" at first, in that port scanning was already a thing, there were multiple available scanners out there. Most of these tools had their own syntax though, and they usually offered one specific type of scan. So nmap came and aggregated everything into a relatively simple tool. It then became incredibly successful and from that popularity nmap got its greatest strengths IMHO : portability, versatility (these crazy options implemented to satisfy super-specific needs) and the OS and service version signatures captured as a collaborative effort over more than a decade!
Thanks Fyodor & team!