I kayak at Tiorati Lake often and love the fact that it isn't open to the public. You must purchase a key to get into the lot that has less than 10 parking spaces. Otherwise, it would be overrun by loud groups picnicing and playing music (like Sebago Lake).
Generally get there before sunrise to see the deer, beavers, bald eagles, etc. As the day progresses, so does the amount of inconsiderate people who don't care if they're blocking the ramp while they blow up their inflatable rafts and have their gear laying all over it. If it were open to the general public - I doubt that I would go there at all.
It is beautiful, as mentioned, lots of wildlife to see if you are quiet enough not to scare it off.
On the weekends there are campers on the far side of the lake who are sometimes loud and obnoxious but I'm able to find a quiet little outlet to relax and reflect.
There are other lakes in Harriman State Park (Lake Welch, Lake Sebago, etc.) but like I've said, the ones that are open to the public (no permits or keys required) are overrun with people playing loud music, screaming kids, etc. If I want to hear that - I can spend the day in the city.