That is a very good question. First we must think about what exactly Judicial Review is. Judicial Review is defined as "Judicial review is the idea, fundamental to the US system of government, that the actions of the executive and legislative branches of government are subject to review and possible invalidation by the judicial branch. Judicial review allows the Supreme Court to take an active role in ensuring that the other branches of government abide by the constitution. Judicial review was established in the classic case of Marbury v. Madison, 5 US 137 (1803). " (pulled directly from Cornell University Law School).
In simpler terms, Judicial Review gives the Judicial Branch the ability to tell all of the other branches, "no, you can't do that." Making it literally the most powerful of the branches. Furthermore, supreme court judges have no effective term length, so they can control the other branches as long as they see fit. It's also controversial because it wasn't explicitly written in the constitution, it was a creation of James Madison in order to expand the power of the Judicial branch of government. He literally wrote it into law that he has more power by justification of something he made up. That is the same logic as saying, "you can't do this because I say so, and I have the right to say so because I say I do." that is why it is so controversial. Now, there are checks to it, Judicial Review can be overwritten, but it is extremely hard to do. I hope this helps enlighten you.