My two cents ( for all they are worth, allowing for inflation)
CoH worked.
Sure it had it's flaws and odd patches. But, by and large, it worked. Not only did it work mechanically (as I expect all published games to do) but it worked for the players as well.
In the six years I played the game I saw every possible character idea wander through the city. Cowboys, Knights, Pirates, Shinigami, Magical Girls, Soldiers, Saints, Savants, Aliens, Mutants, Madmen, six foot Pink Bunnies... and absolutely none of them felt foreign to the game. All of those wildly disperate ideas fit together in a way I havent seen any other game match.
I saw a community that was (and is) one of the most tolerant and open in gaming. It was a community that, on the whole, accepted every playstyle, every character quirk, newbies and veterans. We didn't care as long as people didn't break the unspoken rule of 'live and let live.'
I've yet to find another game where characters stand in the same position for hours because the people behind them are just...talking. If you wanted to hammer away at a TF for the 500th time, it was cool, you could find someone to join you easily enough, but if you just wanted to talk, Atlas Park and Pocket D were always there.
I could fly. Or run, or Teleport, Or leap tall buildings, or be a Coyote or a ninja to get around.
Our city was beautiful. It had a vibrancy all it's own. It was alive in a way that few other games match. The city was a character all by itself, not just a place to sell stuff.
It all worked.