It is funny. I just read some of the previous reviews for Zuma tours, and frankly I'm surprised by the amount of negativity!
Personally, my wife and I had a fantastic time with Zuma Tours. We wen't to Isla Tortuga for the day. The boat was NOT overcrowded, nor was the captain compromising safety.
We started our voyage out of the fishing area in Montezuma. The boat quickly took us over to Isla Tortuga (about a 45 minute ride). Once we arrived there, the captain dropped off the rest of the crew so that they could prepare lunch for us. While the crew prepared lunch, we wen't snorkeling. We got some of the BEST video of our entire trip from this one adventure. We stopped in two different snorkeling spots that both had great local marine life to view.
Once we arrived back at Isla Tortuga, we ate lunch and hung out on the beach. While there we met some Europeans and played some volleyball with them. I felt like a yank. After that we packed up and headed back to Montezuma after a nice full/fun day!
You might be wondering why I gave this an "Average" score above. This is why:
The whole operation is a bit of a tourist trap. Just be prepared for this and it'll be fine.
The boat ride was very scenic and nice, but 45 minutes through ocean swells can be daunting for some.
Even though the lunch was fresh-caught fish, it wasn't very tasty. The crew may be better boat handlers than cooks
The actual island itself (Isla Tortuga) isn't what you expect. In reality, it's a tourist beach. Pretty though it may be, it still had things like rental chairs and the like on the beach. Plus one thing that was a bit strange: Zuma Tours was not the only group on the beach during that time. There were tons of other tour groups also on the beach so it really did seem touristy. In fact, it was the most touristy thing I did in Costa Rica.
All in all, it was totally worth it. The marine life we saw snorkeling was unparalleled, and the video I got from it was amazing. There were just things that could have been a bit better.