Heckerling's central hokum is definitely silly, based on the notion that Mikey (and all babies, in fact) has somewhat adult, slightly cynical thoughts on everything that goes on around him, from conception to end credits -- and that these thoughts and embryonic wisecracks and creative interpretations are heard only by the audience via the aptly cast voice of overgrown kid Willis.
Los Angeles Times
The movie but, rather surprisingly, given the gimmicky premise, it's not gag-me-with-a-pacifier cute nearly as often as it is genuinely charming. [13 Oct 1989, p.12]
Peter StackSan Francisco Chronicle
Look Who's Talking plays baby-picture cute almost beyond the limits of the tolerable, but it has enough spark and intelligence to be a very likable, occasionally riotous romantic comedy. [13 Oct 1989, p.E1]