Yes, it is very fun for adults. It's very much an all-ages sort-of game. It's simplistic, yet requires a degree of strategy. The fact that it was endorsed by Mensa (the High IQ society) is a good hint that it is more than just a regular "kids game."
We purchased this game when our kids were in high school and we still play. Whenever we introduce it to adult friends, they usually go out and purchase it for their household too. My nephew called it "Scrabble without the words"....and it moves faster than Scrabble. More of a level playing field for all game abilities.
I bought this game several years ago, and everyone loves to play it. That includes 5-year-olds who can distinguish colors and shapes, and grandparents who love the challenge and strategies. We can all play it together and have fun with it.
This can be very challenging for adults and yet simple for kids. My husband and I have played this with our 7 year old and we have fun trying to make the most opints possible. Some times you have to look very carefully to find the hidden big points! It is a lot like Scrabble but with colors and shapes. You can stare at it for 10 minutes and then finally find the right spot. Definitely for adults if you are going for a challenge, and yet simple enough for kids who don't care so much about the big points!