A few thoughts: With a relentless pounding Carpenter score, a mounting sense of dread and panic, and a handful of strong performances, Prince Of Darkness should have been an undeniable horror classic, but instead falls a little short due to the ponderous nature of the story and occasional inadvertent silliness. Okay, now I can stop trying to sound like a movie critic. I love the way they blended science and religion together, attempting to bring cold hard facts into an investigation of the supernatural, with these people caught in between logical disbelief and the reality of the horrors surrounding them. It takes a little while to really get going, but this gives you a good feel for the characters and a sense of just how massive the story really is -- in spite of taking place almost entirely in one building. The scenery is cool, the prosthetics are equally as great, and the music really sticks with you. Maybe not among Carpenter's very best, but I still dug it and found it pretty damn creepy and fun to watch.
Who would I recommend it to? Anyone who likes horror blended in with genres like sci/fi and fantasy. Equal parts Hellraiser and Poltergeist.