This question is two-fold. Yes, Wikipedia is valuable as a user-generated encyclopedia of knowledge. However, yes, it is also very prone to errors, or skewed data. People who are fans of something may write one-sided views; people who dislike something may do the opposite. It also contains innocent human error when people think they know something and do not footnote what they write about. Wikipedia should be consulted with a grain of salt, and not for things like research for school. That being said, it does have checks and balances so that it can be edited for errors.
Yes, Wikipedia is valuable. However, I do believe it has a relatively high rate of error. Given the very nature of contribution to the site, there is bound to be inaccurate or simply outdated information. Wikipedia is extremely valuable nonetheless, because it allows anyone to share information for which they are knowledgeable while having endless peer revies for accuracy. To this extent, it is much like a scholarly journal. The only bad part is that the contributors don't necessarily require credentials, and if there are no other individuals who are knowledgeable on a particular topic, then there is no one to review the quality or accuracy of it.