Of the odd numbered Star Trek movies, this wasn't the worst offender. (Clearly, that was Star Trek V: The Final Frontier.) The problem with this movie is that "Let's resurrect a major character!" is a pretty thin premise to hang a plot on. The plot device -- the Genesis planet -- had already been established so it wasn't as ludicrous as it could have been.
Leonard Nimoy's directing skills helped salvage the film; he directed with a fairly deft touch and a sense of humor; note the engine backfire sound effects when the USS Excelsior ground to a halt after Scotty sabotaged it. The opportunity to direct this film, as well as realizing a surprising affection for the character he had been eager to kill off, led Nimoy back into the franchise.
Casting was a bit of a problem, though: Christopher Lloyd, while a gifted "oddball" actor (see Back to the Future) didn't quite have the gravitas to pull off the vicious heavy Kruge, and Robin Curtis was much more generic in the Saavik role than her predecessor Kirstie Alley. William Shatner was at his hammiest: "I...have had...enough of you!" The Genesis set, particularly during the planet's death throes, was barely more believable than the styrofoam rock-laden sets of the '60s series.
In its favor, though, Star Trek III developed concepts from the previous film, helping to create a trilogy that held together rather well. (What a concept, actions and events having repercussions!) The destruction of the USS Enterprise was appropriately dramatic, and DeForest Kelley actually got a share of the limelight. Star Trek III may not be Art, but it doesn't suck.