First and foremost, from one Eagle to another, congratulations on attaining Eagle Scout.
On-Topic: Honesty is something seldom seen, but it's not always something that needs to be heard. It's not a habit/trait that should be broken or kept forever, but just moderated. There's a difference between constructive criticism, and just plain criticism.
First point: I said the same in mine, but I more used that my life would be going in a new direction away from my Troop, but I will still keep the aspects of Scouting with me. It's honest, but it's not saying what I was really thinking, "I like Scouting, and it taught me a lot, I want to leave that Troop because the people there are jerks."
Second Point: I know this all too well. One kid got his project signed off for planting a few trees in a park, which we got done in an hour or so. The park people had to go and redo it anyway because he planted them where they didn't want him to plant them, and he refused to go back and fix it.
I don't really know what to tell you there, except there's a lot of people out there that made Eagle that don't deserve it. But all you can do is to try your best to make sure you deserved your rank.
Third Point: If you see something wrong with a Troop, Patrol, or Scout, don't tell them how it's wrong, say how it can be improved. There is a difference between "They stopped caring about my Patrol" and "Our Troop was short-handed, which made my Scouting career much more difficult within the Troop."
Don't lose the honesty you have, but just remember to choose your words wisely. You can still be honest, but no need to be brutally so.