I found Underdog amusing. My family watched it together, and despite being 21 years old, I still enjoyed it. There were funny scenes that made me laugh, and touching scenes that made my eyes a bit watery. I guess I can expect to be touched and be involved in a movie when it's done by Walt Disney.
The story is okay, the plot is okay. Overall, it's a good children's movie, if you judge children's movie by its own standards. There are lessons to be learned for young children here.
This is great to watch with your family, especially for the young ones. If they've been following the Underdog animated series, then they'll love this real, live version.
I highly recommend this DVD especially if you have young children, buy it!