Slimer's ectoplasm is way cooler. While highly flammable, the psychic goo in The Haunting in Connecticut just looks silky and way too easy to clean up, not like Slimer's viscous green mucus. In a total yawner of a horror flick, it's sad that crappy ectoplasm is the Haunting's one sorry excuse for a hook.
Unless you count the fact that the film is based on a "true" story of a family that was haunted by ghosts in their rental home. Boooooring. Overall, Haunting is grim—populated with characters like Cancer Boy (Kyle Gallner), the family's teenage son who is undergoing treatment for his terminal illness, his Drippy Mom (Virginia Madsen), and his Recovering Alcoholic Father (Martin Donovan). To be closer to the hospital, the family rents a dodgy house, which was formerly a mortuary that was run by a séance-holding necromancer and a psychic Igor who could spew ectoplasm like a true champ. Way back in the sepia-toned olden days, this undertaker and his teenage medium would carve up the bodies of the dead, and cut spooky-ooky words into their bodies... all in the basement of the Connecticut rental house.
Decades later, this dead psychic boy just won't let it go though. He's like "Wah wah wah, the dead aren't at peace, boo hoo hoo." So he starts haunting Cancer Boy—who, thanks to his experimental cancer treatment, is prone to hallucinations, like seeing Slimer harangue librarians (no, not really). But the entire family is a bit dubious of these ghostly visions, of course until the ghosts start putting the smackdown on all of them, too, and then they believe him for sure!
If all this seems mundane, you'd be dead right (ha?). With a cancer-ridden priest (Elias Koteas) there to guide the spirits on their way, the look-alike comparisons to The Exorcist are inevitable, but Haunting is more like that film's unsophisticated backwoods cousin who likes goofy and cheap thrills, while simultaneously boring you to tears with 90-plus minutes of talk about their ailments. In other words, it's as much fun as watching a nagging corpse harass a cancer victim.