For the average person, it was the first experience with a multiplayer shooter. Yeah, there were many available on PC for much longer, but most people had no contact with them. Halo was the one to bring the internet to mainstream gaming.

Other than that, yeah, it didn’t change that much. It did revolutionize controller shooter controls though, more than any game since Goldeneye probably. Gameplay is just standard arena shooter though —maybe a little (or a lot if you’re looking at the likes of Quake) slower to accommodate controllers.