When people say online and how it counts because of much better it became, my mind keeps defaulting back to the massive leap off a cliff in online functionality and freedom from Bnet 1.0 (1990s) to Bnet 2.0 (2010s). Just my personal experience, but online gaming in 90s (and then into the 00s) on PC was awesome.
The answer above me is a good one (Steam). Surprised no one's mentioned support for, and the move to, HD resolutions on the console side of things.