Common Knowledge: No, Underdog wasn't a Jay Ward production, though it's understandable that some make that assumption, given the similar design aesthetic as Rocky and Bullwinkle. Not helping the fact is that both Jay Ward and Total Television used Gamma Production to animate their shows, contributing to the similar styles. Both shows had involvement from General Mills and were syndicated together for years (often the syndicated packages would mix the Ward and Total cartoons up in various orders, further adding to the confusion). Additionally, Underdog was featured as one of the animatronic players at the Bullwinkle's Family Fun Restaurant chain.
Fridge Brilliance: In the "Commander McBragg" cartoons you can tell he's making up his stories because he looks the same in all his flashbacks as he does when he's telling his story. He would've been years younger had they'd really happened.
Harsher in Hindsight: The ending to "The Vaccum Gun" had Underdog humorously fly into the engine of a plane, with no real consequence. In The Incredibles (in which coincidentally enough Live-Action Underdog's VA Jason Lee voiced the evil Syndrome), it's a much different story.
Iron Woobie: Underdog's civilian incognito, Shoeshine Boy, lives up to his "humble and lovable" persona. He's extremely polite to everyone, even the villains. As a result, he gets constantly beat up on by Simon and Riff. But since he does not want to reveal his true identity, he takes every hit. Awww...
Tear Jerker: Yes, surprisingly, even Underdog got one of these moments - "The Witch of Pickyoon". The titular witch places Polly under a spell that will make her sleep for a thousand years unless Underdog does every thing she says. Underdog eventually rebels and manages to (unintentionally) kill the witch by destroying her magic broom, freeing all the people she enslaved... but with the witch gone, there is no way to free Polly from her spell. The townspeople, grateful for their freedom, vow that they and their descendants will watch over Polly for the thousand years the spell will last, and Underdog leaves her in their care, giving her a final kiss before departing. Thankfully, it turns out to be the cure, and Polly wakes up after all.
Underdog: Very well, people, I shall entrust her to you. Farewell, dear Polly, you were always true blue...
Values Dissonance: Underdog's powers come from a "Super Energy Pill". The original purpose was a noble effort to convince children to take their vitamin tablets each night back when flavored children's vitamins were still uncommon (not unlike Popeye with his spinach). Ironically, it is looked at differently today, and it's unlikely a show would depict a character obtaining superpowers in such a manner these days; modern syndicated repeats typically cut the scenes entirely. The origin of said powers also changes to mad science experiments in the film adaptation.
Ensemble Dark Horse: Simon Bar Sinister and Cad Lackey are widely considered to be the best part of the film, largely thanks to them being portrayed by Peter Dinklage and Patrick Warburton.
Harsher in Hindsight: The principal's disbelief about a student calling in sick for Monkey Pox maybe hits a little too close to home following the confirmed outbreak in the UK in 2022.
Ho Yay: "That time when I met that cute poodle and... it turned out to be a guy."
So Okay, It's Average: Really, it's a kid's movie and a live action adaptation at that. The only reason it bombed was basic lack of interest due to these factors. On its own, it's an alright little romp with a few chuckles. And at the least it keeps the basic gist of the cartoon better than, say, Inspector Gadget (1999).
of the classic theme heard in the intro is pretty badass.