Its was incredibly positive for us. Our trainer does classes at the city's activity center. It's a 6 week course ending in the STAR puppy certification. She's a professional handler/trainer, currently works with therapy dogs, etc. I didn't realize it at the time, but from her bio it appears she developed PetSmart's training program. Now, I wouldn't do the PetSmart program at one of their stores, but you can imagine the person that developed the program at a corporate level is good.
Samson was pretty much trained in everything needes to pass the STAR puppy test before the classes, but still benefited. More than anything it taught us how to approach training; enforcing what we were doing right while giving us sone new ideas. It also gave him an opportunity to interact with other puppies around the same age in a structured environment. Because it was done at the activities center the rooms were very large and provided plenty of space. She also organized "pack walks" downtown where her students would meet up on weekends and work on more real life type things. The dogs got used to walking past outdoor diners, going into stores (there are several pet stores and other places dogs are welcome), seeing unfamiliar dogs while on a leash, and being pet by strangers. Again though, it was more about teaching the owner to train than teaching the dogs.
I know there are some pretty string and differing opinions in this, but if it ia thr right class, setting, and instructor it will be a positive experience.