Are IQ tests a reliable indicator of intelligence and does IQ really matter in life?

No it doesn't. IQ doesn't measure critical thinking. Someone can learn an IQ test, be more familiar with it, this doesn't measure intelligence. Someone who practiced them more would get higher marks then someone who didn't. Someone can be intelligent without being good at formal tests. Einstein is a famous example, he was dyslexic and failed his school exams, but went on to become one the greatest physicists ever, you can't measure the imaginative thinking that was needed to come up with his theories of relativity. Einstein used to imagine himself riding on beams of light, and applying his normal knowledge of physics from this standpoint to see how it would contradict. Standard tests frown on this kind've thinking.