We have had the Peg Perego Polaris RZR for more than a year and it still brings miles of smiles to my 4 and 6 year old every time they drive it. We have had several Power Wheels and Peg Perego vehicles, but the RZR is far superior to all of them, and it's still faster than an 18V Power Wheels. Run time on the 24V battery is good (about an hour at full throttle), but it wouldn't hurt to have a spare battery on hand. Leg room for a taller or older kid can be a bit tight, but it still has far more leg room than the Gator and most Power Wheels. The radio and MP3 jack are cool features, although it's far too easy for kids to leave the radio on thus draining the AA batteries.
The RZR is pretty rugged and has never suffered any significant damage jumping off curbs or generally being abused. The working rear suspension really helps to smooth things out, although you should pay close attention to the plastic pins that secure the lower end of the shock to the trailing arm. Mine had a habit of coming out so I replaced them with a real nut and bolt. Problem solved.
Although the truck is really rugged, there are still alot of plastic parts that will break if the truck is really abused. For instance, the plastic brush guard on the front breaks fairly easily if you run into something, and the faux lights on top of the roll bar are a bit flimsy, as is the roll bar. Finally, the latch on the 'seatbelts' is not very rugged, so if you use the seatbelts, which you should, plan on having to replace them from time to time. Parts for this thing are really inexpensive.
The truck is really safe for both driver and passenger, and we have never had a kid fall out or otherwise get hurt driving or riding in the truck. At $699 the RZR is not cheap, but it goes on sale at Toys R Us from time to time. Peg Perego has been fantastic when I call them with warranty issues or need parts, and their willingness to back this product is one of the reasons I recommend this toy so highly.