For $18, I felt like I got maybe an $10 experience.  The entire reef is much smaller than I thought.  You start off in a jungle like atmosphere (hot and humid).  As you wind down a stone pathway, you will see signs from the Monterrey Bay Aquarium about conservation and such.  I saw it more like propaganda.  One curator was standing by the piranhas.  She wouldn't talk to anyone unless if you asked her questions.  She was very matter of fact and short with all the visitors.  Nothing really stood out.  They have two tunnels to walk through where you can see the sharks which is pretty cool.  The stingray pool and jellyfish tank were OK I suppose.  If you're a fish fanatic like I am, you will be greatly disappointed.  On the other hand for parents, this is a great way to entertain the kids in Vegas.  I'm glad I didn't drag any of my other friends with me.