Review days in class can be extremely helpful in helping students identify the critical information they need to know for their exam from all of the information we've been throwing at the for the past unit. Many of our students struggle finding that important information on their own. Main ideas, key concepts, trends, and other information is difficult to find if you don't know how.
Make it fun. Play a game. Resist the urge to just teach to your teacher made test. All of the information on that test is important, but not more important that teaching your students to go find and learn it rather than just memorizing the information that you put on yoru test. We're building life skills and we're training people. Life doesn't stop at the test, it starts there. If test day is supposed to be the best day, then it's important to have a good review, or the day after test day will be the worst day.