I played it for about a year and a half when it was new. It had a pretty decent following though nothing anywhere near the level of something like WoW.
It was really fun though especially during a "bane". For those who didn't play, a bane was when you effectively declared war on someone else's city. Once set up, each side was given a set amount of time to prepare (like a day or a week or something, I forget) and then once it went off, all of the town's buildings were vulnerable and if you destroyed their tree of life, their town was taken over by the other team. Shadowbane wasn't about gold, loot or missions though there was plenty of that. It was about full on guild vs guild battles. I've never really found a MMO with quite the same experience. So this is very sad for me even though I have no time to play a game like this anyway.
Ultimately, I think it was killed by griefers, people who didn't like PvP leaving the game and constant crashing that they didn't fully fix until about the time I stopped playing.