As a genre? I would say no. Cyberpunk is usually described as a capitalist dystopia in which a handful of companies supersede government powers and wage wars against each other beyond the concepts of national borders. In addition, cybernetic enhancements become commonplace, as a way for companies to extract more value from their workers. Cyberpunk stories usually are about groups rebelling against the system through organized crime, who ultimately fail to escape the underlying system of capitalism, doomed to repeat history time and time again.

HL2 falls in none of the genre stereotypes. While it is dystopian, it's not capitalist, so it's not "punk" and it isn't "cyber" either because of a lack of commonplace cybernetics.