Roger Ebert:
A movie like this is a deep mystery. It asks the question: What went wrong? "Clifford" is not bad on the acting, directing or even writing levels. It fails on a deeper level still, the level of the underlying conception. Something about the material itself is profoundly not funny. Irredeemably not funny, so that it doesn't matter what the actors do, because they are in a movie that should never have been made.
...
But Martin Short is clearly not a little boy. He is a curious adult pretending to be a little boy, with odd verbal mannerisms, like always addressing his uncle with lines like "Oh, yes, My Uncle!," and fawning up to strangers like a horny spaniel. If Clifford is not a real little boy, then what is he? The movie doesn't know and neither does the audience, and for much of the running time we sit there staring stupefied at the screen, trying to figure out what the hell we're supposed to be thinking.
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It's not bad in any usual way. It's bad in a new way all its own. There is something extraterrestrial about it, as if it's based on the sense of humor of an alien race with a completely different relationship to the physical universe. The movie is so odd, it's almost worth seeing just because we'll never see anything like it again. I hope.
https://www.rogerebert.com/reviews/clifford-1994
God, I miss Roger Ebert.