Yeah, it's thirty years old. And you probably have it on DVD or Blu-Ray, or you can watch it right now on your computer or your damn phone via your Netflix account.
But oh man, does it look good on the big screen. The 4K digital projection is stunning; the amount of detail is astonishing. Tiny visual elements like the headlines on a newspaper clipping ("GHOSTBUSTERS PINCH PUNK POLTERGEIST"), or the moving lights on the Manhattan backdrops, or the interior of the Gozer Temple (yep, there's an interior!) just pop out. Ghostbusters was one of the last big Hollywood releases to really use the 2.35:1 format before studios and directors started to worry about what their movies would look like on home video, and seeing the boys standing shoulder-to-shoulder in non-"TV safe" widescreen is truly awe-inspiring. (It's also pretty cool to see shots of downtown New York and realize that it isn't Toronto or St. Louis.)
And it's a great movie, too. I mentioned this earlier this year in a comment on a story about '80s movies, but it bears repeating: The terrific thing about Ghostbusters is that, unlike a lot of today's event films, it doesn't burden the characters with pointless backstory or arcs. You can pretty much figure out who these people are just by seeing them in action for a couple of minutes. Each performer brings his or her strengths to their part. It's also a rare genre movie with terrific worldbuilding that's also a hilarious comedy. The story takes the Lovecraftian/SF elements very seriously — it wouldn't surprise me at all if Aykroyd knows exactly who the Meketrix Supplicants were, or why being "large and moving" makes a Torb especially terrifying — and the humor arises out of that conviction, not in spite of it. Apart from one gag — arguably the greatest sight gag in movie history — the comedy is almost entirely situation-based. (Incidentally, it's also what makes Guardians of the Galaxy great — there's a big universe and complex character histories, but the movie gives us just the parts that are really relevant to the story.)
Ghostbusters was only intended to run during the week of Labor Day, but in a lot of markets it's been held over for another week. Go see it, especially if you've only ever seen it on video. You won't be disappointed. (And go see it at an Alamo Drafthouse if you've got one in your neighborhood — the impressively-curated vintage toy and cereal commercials and related videos running before the show are worth the price of admission alone.)