Twister is your typical special-effects-laden-summer-fluff-edge-of-your-seat sort of entertainment. If you can put aside the implausibilities (such as being able to have a tornado pass over you without being hacked to pieces by the flying debris), it is an enjoyable diversion (being an Amblin Production, I also found it interesting that there were no annoying smart-ass kids in the movie, a la Jurassic Park and its follow-up, The Lost World coming out next year) that is nicely-paced and with well-conceived and coordinated camerawork.
What I found particularly interesting was the relationships-as-tornadoes subtext. Of course, one of the emotional cores of the film was the Jo-Billy-Melissa love triangle, which provides a nice basis for this metaphor. Like the freak force of nature, relationships are unpredictable, potentially destructive, and yes, they have their beauty too. Jo and Billy, at the beginning of the film, are about to finalize their divorce (I know, this was the basis for "Outbreak" and "The Abyss", two other disaster movies). It is implied throughout the film that their marriage was tumultuous. While Jo still seeks to hang on to the memory of the tumultuous relationship (chase tornadoes), Billy has decided to settle down in a somewhat stagnant relationship with Melissa, a bland therapist, and take a safe job as a weatherman. However, as the story develops, he realizes that it was his relationship with Jo, despite the turmoils, that gave his life meaning (chasing tornadoes). And as they try to drop an instrument package to study the inner workings of tornadoes, they both come to an understanding of the inner workings of their relationship. Melissa leaves, unable to deal with the danger of the tornadoes that pop up without warning. However, there would have been more emotional resonance if Melissa was a strong character like Jo, instead of the comic foil ("what's a tornado, Honey?"). In the end, Billy sacrifices the vestiges of his new life in order to choose the growth experience of the not-so-serene relationship with Jo-- his new fiance, his new truck, and finally, his new job. In the end, amidst the debris left by the tornado, Billy and Jo decide to start again (out of every potentially cataclysmic relationship, there comes data to be analyzed, lessons to be learned, and growth).
But then again, it could be just a movie with a lot of really cool shots of big things being thrown around and stuff getting blowed up real good.