I have watched many versions of Winnie the Pooh, from the A.A. Milne originals to the more recent "New Adventures..." to the Book of Pooh. A Piglet Movie is much more A.A. Milne, which I personally find refreshing.
The storyline is very gentle, and the feelings evoked by the themes are very familiar to small children (being too small, not being noticed, being lost and frightened). Each short story within the film was carefully chosen and fit perfectly with the overall theme. The search for Piglet and his magical scrapbook tie them all together seamlessly. The folksy Carly Simon music may not be some people's first choice, but it just works somehow in this movie. Just right.
This movie has just the right amount of humor and excitement to hold a young child's interest without overkill. There were a couple of initial moments of nervousness for our 2 and 4 year old, when the bees were chasing Pooh and his friends, and again when Kanga gives Piglet a bath and Piglet is clearly terrified. My children have since relaxed, as they now understand these scenes a little better, but it may help to explain what's happening to little ones.