Yes, the acting was superb – including a strong performance from Roddy MacDowell, who turns out to be something of a hero. I think this film came out the same year as The Exorcist, which distracted viewers from this excellent horror film.
I found Matheson’s script-discussion of different kinds of mediumship (mental vs. physical) literate and fascinating. The effects were good for their time – Dr. Barrett’s exploding coffee cup is a classic in nerve-jolts.