I thought it was lame and a stupid attempt to make a live action movie out of a cartoon.

Going by movies like the Hulk, etc this was pretty good.

I would really have to disagree with you. This was a lame attempt to take a 20 year old cartoon that has been off the air for almost as long and turn it into a movie. Movies like the Hulk are made because the character is still immensely popular. Most kids nowadays haven't even heard of Underdog, let alone watch the cartoon.
Personally I've never been a fan of cartoons turned into live-action films, it takes away from the original concept to me.