I saw Mystere in Vegas a couple weeks ago. It was a great show.
Mystere is Cirque Du Soleil's oldest show in Vegas. It's been running at the TI, often playing to sold out crowds, for more than 10 years. Like all Cirque shows, it is a mix of music, song, acrobatics, gymnastics, dance, and artsy stories.
This show is more primitive than other Cirque shows. The theme is not as tightly woven into all the performances as it is in other shows. The theme is more of a broad framework into which they drop different acts. It seems that any act could easily be replaced by another on a moment's notice.
The performers also where less clothing than in other shows (except, I imagine Zumanity). It's nothing that would violate most local ordinances, but it is different. There's simply a lot more skin.
At the end of the show, there performers remove their masks and wigs for the curtain call. They are allowed to be seen as individuals and "normal" people on stage. Normally in a Cirque show it seems individuality is discouraged to maintain the effect of the otherworldly story they are telling on stage.
The performers acting as spotters in the acrobatic maneuvers are more obviously acting as spotters. And the acrobats themselves did make a few mistakes.
Overall the performances was fantastic, however.
There is more crowd work and audience participation in this show. The clown wanders about to entertain the audience. If you don't want to take a chance on being part of the show, avoid the first and last rows of the lower section of seats. Also avoid the aisle seats. You may want to avoid the lower section altogether.
The crowd work itself was a bit risky. They put some folks in embarrassing situations. They sprayed one woman in the face with water (soaked her pretty well, too). At one point the clown reached down the back of one girl's dress, fiddled with his hands, and pulled out a bra, which he then twirled around. Of course he had palmed it so he was not actually involved in disrobing her, and it got quite a laugh. But it was a bit risky, especially since she looked to be only 14-17 years old (though I am pretty bad at that guessing game).
When it was introduced in 1993, the show was edgy and completely different from anything anyone had seen in Vegas. It ushered in an new era in Vegas entertainment, and spawned other hit shows in the Cirque family (O, Zumanity, Ka, and Love).
It still has that feel. It's more raw and not as refined as the more recent shows. This must be a choice they've made because it could have adjusted in the past ten years. But it looks today much like it probably looked when it opened.
If you are attending your first Cirque show, go to Ka or O first. You will be amazed and the skill and technique on display. If you are a Cirque fan already, and haven't seen Mystere yet, go see it. It is valuable not only as a great show itself but in understanding the creative evolution of Cirque Du Soleil over through the year.
In other words, it was a great evening.