It's a cunning ploy to drop the crew of the Enterprise back in the 20th century, since it's a lot cheaper to film in modern-day San Francisco than fabricate three hundred years into the future. Indeed, there seems to be a lot of money-saving techniques here - we get effect sequences recycled from both the previous two entries. Still, it's hard to complain when the culture clash on view is such fun; seeing Kirk and co. struggling with money, swearing ("double dumb-ass on you!"), crossing the street and the archaic technology which is the computer mouse, is a joy and delight.
Less successful is the unsubtle ecological message, which could have made its point in four words (Killing Whales Is Bad), but hangs around for most of the movie. Amusing to note the makers had to use animatronic whales for 95% of the footage (and very impressive they are too, I have to say), the real thing presumably not deemed suitable... The lack of an actual enemy is also a bit of a problem: much like Disney, Star Trek has had some glorious villains, but here, the major threat is Californian drivers. Bad, but not quite the wrath of Khan. No real matter, when rarely has the Prime Directive - y'know, the one about non-interference - been so gloriously raped as here. By the end, the Earth has gained a phaser and a communicator, discovered transparent aluminum, and lost a biologist. Sounds like a fair exchange to me.