They did it again: ripped off an old show's title, then destroyed the nostalgia with boring "re-imagined" stuff. The '60's cartoon was one of the funniest of its time, a good-natured satire of super hero comic books. The character was drawn as 1/2 way between animal and human, the way Mickey Mouse is. Here they use a real beagle; that's about the same as making a Mickey Mouse watch with a real rat.
Most of the clever schtick that made the original show funny is missing from this film. Instead, we get a clumsy ex-police dog who's even dumber than Cad. And some pet owners who add nothing to the story. Cheesy effects (the dog-talking animation is embarrassing). Poor scripting. A stereotyped dwarf playing Simon Bar Sinister. The gravelly noise box guy they hired to voice Underdog is painful. You'd think they'd at least gotten a voice impressionist to approximate Wally Cox's humorously distinctive voice for Underdog. But no. There are, at least, a few affectionate references to the source material (such as the rhyming lines), which lift it to a 4.
Only small children that love dogs may enjoy this. Everybody else should get a DVD of the original cartoon series. Watch this only in desperation.