I would like to add a little to the excellent answer from Madara.
The reason why you get more negative reviews is because the rusty wheel squeaks and some square pegs don't fit the round hole. Some brilliant people have been a part of Stack Overflow, but not all of them have the best personality or play nice with others.
Sure, you can pick holes in the reputation system and the moderation system - but then again you can criticize just about anything on this Earth. The guys behind Stack Exchange have learned a lot over the last five years and have put together a lot of help and easy to read material on how to use the site. But you know what? You simply couldn't count the number of lazy or incompetent new users who don't bother to read that material, and don't bother to do even the most basic of research before they ask the most basic/oldest/laziest question you could imagine.
Happy users don't tend to write nice happy blog posts stating how much they looooove Stack Overflow - because they just keep on using it. A lot of the people who dedicate their time to answering questions are busy professionals who are paid good money to be doing actual real work - but they donate time and expertise to this site free of charge. Next time you read a negative review, remember that our job here is not to endlessly baby users who are too hopeless to help themselves, or endlessly answer the same questions, or allow users to use it to shoot down others to further stroke their own egos.
Like any good or complex tool, Stack Overflow can take some time to learn how to use. People who charge in and use it recklessly are liable to lose their fingers (figuratively speaking). Take your time and use it wisely and pretty soon you'll be sucking the rep koolaid up there with the "StackOverlords".