A few thoughts: If you believe in ghosts, look through the red viewer -- if you don't, look through the blue. Welcome back to the wonderful world of William Castle's gimmicky horrors. And when I say wonderful, I really mean it, as his are some of the most entertaining and light-hearted horror movies of the era. Unlike several of his more popular films, this isn't one that could ever really scare anyone or even creep them out, but stands out for the creativity of the gimmick alone. The acting, cinematography, story, etc. are all pretty average, with the major standout component (apart from the blue/red ghost scenes) being the lighting, which I always enjoy the look of in his movies. Obviously this isn't on the same level as House On Haunted Hill or The Tingler, but this was never intended as a standalone movie. It relies heavily on audience participation, which does make it suffer when watching it at home. I would strongly suggest trying to get your hands on a few pairs of old red & blue 3D glasses and watch it that way, but it's not required.
Who would I recommend it to? Only people who can appreciate light, fluffy "horror" that isn't particularly creepy, but just pleasant to watch.