I've been vacationing at Higgins Lake my entire life. When I was young we would camp there. Around age 7 my family bough a house on the lake. It is my favorite place ever, and has something for everyone.
There are two state parks on Higgins: North State Park and the South State Park. Both are fantastic. The South State Park is the largest State Park Campground in Michigan. It's fun to take the boat there for the day. There is always a lot of partying and people watching. It's a good family place too; where my family camped before we had a house there. The North State Park is more low key, but close to where they do the fireworks on the 4th of July weekend.
There is also a sunken island on the south end of the lake, and a real island with sand bar on the north side of the lake.
There is a ship sunk in the lake on the north side of the lake (near the north state park) which is great for SCUBA divers.
Higgins lake is crystal clear, and one of the most beautiful natural spring fed lakes ever.