Apparently Wildstar isn't doing too well. It's losing players at a rapid rate and is switching to a single megaserver. There's a 700+ comment thread at Massively discussing the issue. Massively blames it on the focus on raids and very difficult endgame content.
It's interesting to watch this from outside. I was in the Wildstar beta, but did not get the game at launch.
However, I'm not so sure that raiding and endgame are to blame, precisely. Sure, it's where a lot Massively readers--who are core MMO gamers--washed out. But my rule of thumb is that there are people who are ten times better than you are, and people who are ten times worse than you are. If the core MMO gamer group washed out at endgame, where do you think the casuals washed out?
I think the basic leveling game was too difficult. I actually wrote a post on the Beta forums when I was just level 15 or so, saying "I don't think I'm good enough for the game you are making." I found that just basic leveling quests in the Wildstar beta required a lot of intensity and avoiding telegraphs. I think having that reaction--for a fairly experienced gamer--at level 15 was a bad sign, because the game would only get harder.
Personally, I think it's instructive that two of MMO success stories of the past decade, WoW and FFXIV, have featured very simple leveling.
I also think Wildstar suffers from the "veto" problem. Let's say that you have a group of friends who want to go out for lunch. You have to find a place which all of you can agree to, or at least a place that no one cares enough to veto. I think Wildstar was different enough--both in tone and mechanics--that many groups had one individual feel strongly enough to veto it. And that means that the entire group falls away from the game.
Of course, though, this is just my view as an outsider and beta tester. Perhaps those of you who played the game at launch or over the last few months have a different perspective.