I'll admit I was worried about "Dear Mr. Watterson."
Judging from the preview, it seemed as if the filmmaker's heart was in the right place. But you never know.
Well, I watched it tonight (via On Demand) and was not disappointed.
I wouldn't recommend it to someone who was not a "Calvin and Hobbes" fan. To such a person, I would suggest therapy.
But if the groundbreaking comic strip meant/means something special to you, I think you will find the film's tone agreeable.
I still plan to see it when it comes to The Magic Lantern (a week from tonight, I think). But if you go ahead and watch on cable, here's a hint. Stay with it to the very end of the credits.