My almost 4-year-old son has been going to an all-day Preschool since September, and he loves it! I wanted to get him into a preschool program because we live in a pretty isolated area and he doesn't really get to spend much time with other kids otherwise.
Before I enrolled him, I set up a meeting with the lead teacher of the program and asked her a million questions. What is your typical day like? Is there a naptime? How do you handle the kids who don't nap? (my son is NOT a napper). How is inappropriate/bad behaviour addressed? How often do the kids get to play outdoors? What kind of activities do you do? etc... I felt really good about the program after speaking so extensively with the teacher, so I was happy to proceed with enrolling him.
I think that is really the key--if you feel good about the program and feel like it is a good fit for your child, then go for it! If it doesn't feel right, then maybe it isn't the right place to go. (FYI--my son has truely thrived at his preschool! Every morning he wakes up at the crack of dawn and excitedly asks "Am I going to school today, Mom?!")
I hope that you find something that works for you and your son!