My mother in law and I tried the Sea Trek in Underwater World, it was fun!
Compare to the other diving activities, we choose this activity because the price including the admission, Sea Trek and a tropical drink, and we don't need to be in the sun and get to be very close to amazing marine life! I'm a diver, but I found this activity is really fun, because it's easy and get to have close encounter with sharks, turtles, and rays, they will come up to you to check you out, so it's pretty cool!
It is quite different to see the sharks, rays and turtles from inside the tank than from the tunnel, after the Sea Trek, you get to take a hot shower and you can go through the aquarium to see the rest of the place, we spent a long time in the tunnel, because it's quite soothing to sit there watch the fish.
Not too bad for a small island like Guam! :)