Yes, it's wildly uneven, but can you fault a movie with Kevin McCarthy as Miles Bunnell, The Mutant from This Island Earth and Mary Woronov? It's a Joe Dante film underneath all the misbegotten cross-breeding and that is a beautiful, anarchic thing.
Back in Action does have a creative spirit and propulsion, but it misses the gleeful anarchic combustion of the best Looney Tunes. They were also disciplined, informed by theory and executed with precision. Some fleeting moments, such as the scene at the Louvre, contain postmodern elements that might gesture towards the genius of Duck Amuck or Dante's own Twilight Zone short, but mostly the film is simply not funny.
A strange product. Aesthetic harmony seems to be the least of Dante's concerns. The movie works only because it pulls off each of its demanding gags, materializing its "looney" ideas even amid such a superficially bland (though totally ruled by cartoon logic) reality.