Watching this movie 25 years on, it still works. Obviously the onward march of technology has rendered several of the central plot devices redundant (although, to be honest, most modern techno-thriller entries are far less plausible) but the sheer tension of the story grabs you almost from the off and never lets go - there aren't many genre movies that got an Oscar-nomination for screenplay, which amply demonstrates its quality.
And the last ten minutes or so are still jaw-dropping. That spectacular (if implausible) NORAD set is as astounding as ever, and the last line still deserves it's place in the pantheon.
Laugh at the antiquated tech by all means, but be impressed by the effort taken to make it feel believable (cf. the sequence where Broderick's character gets the password for the school computer.) Hacker movies have rarely come this close to being real - and, as someone who had been there and done that at about that time, it was scarily right.
In no way is this one of the greatest movies ever made. But there's no question that it achieves the rare quality of transcending it's genre.