I'll be honest and say that I'm a stealth camper and this review was written from that perspective. It isn't by choice, mind you, it's just that coastal MA has very few places you can legally camp in peace (away from all the families and drunken college kids) and the prices many parks/campsites will ask per night is just ridiculous if you're like me and don't intend to use their power, showers, bathrooms, etc.
So with that being said, this park is definitely not the place for someone like me. The paid campsites they have available are exactly what I described above: little to no privacy, lots of loud kids, lots of loud 20-30-somethings definitely not drinking in a dry park late into the night, and reservations (that need to be booked before 2pm the previous day, even if open lots are still available) starting at over $20 a night when adding tax and "handling" fees. Now technically speaking, camping in the park off-campsites isn't prohibited (theres no posted signs or regulations on their website or at the park headquarters that explicitly say you can't, nor any state laws against it - I've done my homework as I don't want to be arrested), it's clearly frowned upon given my observations in the numerous times I've camped here. Local police fly up and down the main roads and bike paths (which is super dangerous) through the park all night, flash their searchlights through the woods, and sit in parking lots revving their engines like teenagers with their first car. The place really doesn't give off a welcoming vibe. I get that they might be trying to scare off any homeless people who take refuge in the woods, but if those are the methods they're using I really don't wanna see how they would treat someone if they caught them.
So if you're like me and would rather just go find your own quiet spot to camp out for the night by a small fire, even if it meant slipping $5 into a box by the entrance, look elsewhere. Myles Standish State Park is not the place for a lonely night in the woods. I've only been able to keep coming here because I camp responsibly, I keep a low profile, and I live about 20 mins away so I come in by bicycle. If I had better options I'd go elsewhere but driving to western MA, NH, VT, ME, or even NY where dispersed camping in state and national parks is more commonly allowed just doesn't make sense when it's only for a night or two.
TLDR: if you like solitude in nature go somewhere else if you have the means to, if you don't have the means to then stealth camp - just don't do anything stupid and screw it up for the rest of us!