Crystal Lake is a clean, spring-fed lake unlike many E. Coli lakes in the lower peninsula these days (I recommend staying away from nearby Pentwater beaches on Lake Michigan as there was garbage floating in the water there and I got an ear infection). The area is very rural but the nearby town of Hart has quite a few good restaurants, and Michigan's Adventures, Muskegon, and Silver Lake are nearby if you want to make day trips. Overall, this rental was very quiet, with most neighbors gone in August. We were the only swimmers in 7 days there, and used the pontoon and pedal boats quite a bit.
There's also excellent star-gazing and I loved the smell of apples and cherries ripening as I drove in the area. The Hart-Montague bike trail is nearby, with an excellent bike rental (The Wood Shed) in Mears if you don't want to tow your own there. I'm a writer and created a short book and pirate treasure map so that my daughter could find toys I'd hidden along the trail. I know misdirection is in some ways wrong, but she loved it. I think she'll remember this trip all her life.