Let's start with the contradiction that is this game: Mysterium is a cooperative, one-VS-many board game. If you don't know what that means I'll try to put it simply - In most one-VS-many games, one player plays against the rest who play on a team (they very often use the "heroes VS the dungeon lord bad guy" kind of story). And in cooperative games...you work together, hopefully you knew that one. So in this game, the one player isn't trying to defeat the many, but is helping them succeed.
Players only have a certain amount of time to make guesses, and only a certain amount of turns to get all of their clues or else they lose automatically. Plus, they only have pictures, which they can not show to other players, to figure out the mystery. These elements make it not only more interesting than Clue (because rolling and moving gets pretty annoying) but also make deduction more difficult so players really have to work together in order to succeed.
I'm not usually a huge fan of cooperative games (I like winning, and having the win to myself, sue me) but this game changes everything. Mysterium has plenty of teamwork but doesn't allow for an "alpha player" (someone who makes all the decisions for the group in cooperative games). It's fun and challenging, and I love a game that makes me think a little more than normal.
The art style is also gorgeous in this game, which is another reason I like it so much. The colors are vibrant and the cards are so detailed that every time you play you could find something you hadn't noticed before! (Yes I'm excited; you don't understand how cool these cards are!)
What's also great is that there's so much replay value in this game. (I should know, I played it 5 times in one weekend). Not only do different cards get drawn for the mystery every time, but the ghost also changes every time (or it should - give everyone a turn okay?). People look at things in different ways, making it essentially a new game every time, because you have to get inside other players' heads and figure out what they notice so you can notice it too.
If you haven't already caught on, I highly recommend this game. Like actually, go buy a copy right now and call your friends and play for the rest of the day, because it's awesome. I recommend it mostly for medium-sized groups (4 or 5), and for anyone who either loves board games or really wants to start getting into them. It's even great for families and kids because it's easy to learn and play and can teach them a lot about context clues. I promise it is well worth the money because it will entertain you plenty of times.