Most people don't like my answer but it's the truth: if it's legal and doesn't need to be issued by a doctor...then it's probably a waste of money. The only exception being if you have deficiencies in your diet and need to "Supplement" (hence the word) what you aren't getting from the food you're eating.
Protein powder is a convenience tool for me. I eat it when I don't have time to make a meal. It offers me no benefits as I get plenty of protein from the food I eat.
There are studies that do show the effectiveness of creatine supplements. However, you shouldn't expect any significant gains from taking it.
The fact of the matter is that people will always abuse substances of any kind (ex: take 3 pills instead of 2). If a supplement actually works, that creates a dangerous and potentially lethal situation. In contrast, if it doesn't create a significant danger then it's probably not that effective. It's for those reasons why I maintain my mindset that legal supplements aren't worth my money.