"I'm a big believer in the fact that opinions are really important, but people's justifications for why they hold opinions are basically crap."
- Game designer Simon Strange (from Atari's series of Godzilla fighting games and the upcoming spiritual successor Kaiju Combat) explains in an upcoming Gamasutra interview that you should always listen to your players...to a point.
Your players are good at knowing when they don't like something. That part comes naturally. But being able to explain exactly why they don't like it is a really unreliable data point.
"When someone says 'I don't like this,' that's really important and you have to believe them. But when someone says 'I don't like this because-,' you can often kind of ignore their 'because,' because they often don't have the data to understand what's going on," he says.
This bit of wisdom seems especially apt for the smaller developers among you, who might rely on verbal feedback more than on hard data. Always, always listen to your playtesters when they don't like something, but dig a little deeper than their own opinions to figure out why.