Far too many folks, I fear, list this as one of Warner's worst. That is where I come in, to bolster it a little. Sure, there are the shortcomings,such as Hal Smith, despite his best efforts, failing to approximate Arthur Q. Bryan's voice qualities, and its being a late McKimson-Pierce outing (McKimson's two directorial colleagues still turning out a few very good ones into the 60s).
But, surprise, surprise, McKimson has hit on a great (one-shot) character creation in Rupert; he carries the day. This director never was strong in pantomime humor, but he achieves it in the canine character. And he's helped along by strong personality animation (Bonnicksen? Grandpre? Tom Ray was doing the close-up speeches by this time). And the film's climax, where Rupert takes Fudd on a drunk-driving spree, is a comic high point.
It definitely has its moments.