TripAdvisor has led me astray on many occasions (usually restaurants). In this case, however, the 5 star rating is well deserved. As I had mentioned, this is the most fun I've had on 4 wheels, but also definitely 1 of the top 5 most fun things I've ever done in my life :D
This was only my second time on an ATV (1st time in Florida), and I'm hooked. This is definitely not for the feint of heart. If you're relatively strong or athletic though, you'll be fine. If you're a total couch potato or the very nervous type, go on a UTV. It costs a little more, but 1-4 people can go on one. Even if you're not driving, I think it will still be thrilling, and the scenery alone makes it worth it. (I don't think you'll get this scenery unless you go off-road.)
You'll get all sorts of terrain - from flat dirt to mud, to small rocks, big rocks, and everything in between. This is AZ, so the trails can have some steep uphill and downhills (like 45 degrees +). Some parts of the trail were very technical (rocky with steep climbs + tight turns) - so just go slow, and trust yourself and the machine.
Kate - our guide - was really awesome. She was very professional and patient. She went at our pace, so it really helped with the nerves. She'll pick up the pace once she sees you're more comfortable and confident. She checked on us to make sure we were comfortable and hydrated. I definitely recommend her!
The scenery was so beautiful. The trip was 2 hours, which in the beginning seemed like a really long time. But I wish now that it were longer.
Some tips for newbies like me - try to relax. Stand up if you feel unstable (which is all the time :D). Try not to death grip the handles (hold the left bar by putting your pointer finger over thumb - this will help save your forearm). Grip the seat of the ATV with your knees when standing, thighs and knees when sitting. Heels down always.
I did the sunset ATV tour yesterday. You first gear up and go on a practice course, then off you go!
It was for sure hot, but it got much cooler. I drank a ton of water throughout the day to prepare and during. Don't go on a full stomach or a totally empty stomach.
I wore very light hiking pants and a short sleeved shirt. It worked pretty well. I was very nervous prior to the ride, and thought I needed to wear long sleeves and heavy pants, but it's really not necessary unless you're a speed demon/reckless.
I personally wouldn't wear shorts though if you're on the ATV; I would think that if you get sweaty, it might be harder to grip. I wouldn't wear tight jeans either - too constricting. Close toed shoes are a must; I wore hiking boots and they worked great.
Enjoy!