For me, I find that user reviews tend to be much more in line with my own opinion of games than "professional" reviews.
The only "problem" is it's possible for developers/publishers to do something to piss large amounts of their playerbase off, which will tank their user score, such as in the case of Diablo III. Is this a bad thing? I don't think so. Companies shouldn't be doing stuff to piss off a huge enough amount of their playerbase that they end up with a 3.0 user rating in the first place. The most sad thing is that most of those people pissed off and disappointed with the game already bought it, so the game sold millions and is considered a huge success despite its massive flaws and alienation of long-time fans.
Developers have the internet as a powerful tool to get feedback from their customers and see what they did right and what they did wrong. It is foolish for developers to dismiss user score as "useless" when a low user score should be a red flag that something about the game really upset or disappointed the players and should be avoided in future games.