Just beat the Wii version. It's pure awesome. The gameplay is really good (the Wiimote just feels right as a proton pack), and the graphics are a nice hybrid of the movies and the cartoon style.
But best of all? The story and acting are top-notch. These really does feel like an interactive Ghostbusters III. Aykroyd, Ramis, Hudson, and Murray all slip into their old roles like they'd never stopped playing them, and Annie Potts and William Atherton also return to spice things up. The writing sparkles, with a plot that is both original while also connected to both of the movies (resolving a couple of unanswered questions from them both along the way). All of the Ghostbusters have great dialogue, too.
Perfect? No; there can be a couple of control issues, mainly while trying to navigate objects through doors. But it's pretty close. If you enjoyed the movies, buy this. If not, rent the movies, then at least give this game a rent as well.