Unless you are talking about achievements or perhaps lower pings, I don't see what you're talking about with "evolution in online play". I don't see any big improvement in online gaming between say, Quake, and Call of Duty 4.
Not that online games today are worse than they were a few years ago. I think they're about the same.
Anyway, what I do think is that online gaming isn't so much about the gaming but rather about the socializing. The difference between, for example, Xbox Live and Canasta isn't the game that is played but rather the social groups the different activities appeal to.
I'm not just talking about achievements, I'm talking about the whole layout of XBL. Arcade games, the easy to use Mic system (no downloading Ventrillo or TeamSpeak), text messages, voice messages, the Marketplace as a whole, easy way to invite friends to games (click name, click invite). There's a lot more to XBL than achievements.