I won't add to the accumulation of complaints about the quality (or lack thereof) of the DVD: wretched colors, non-existent contrasts, awful soundtrack. However, the whole thing remains watchable and therefore my rating is purely artistic and based on the perceived quality of the movie. At the end of the shooting of "The Raven", there was some time and a little bit of money left so Corman kept Karloff and Nicholson, recycled sets and costumes, and produced this "Terror" in several days.
To be fair, considering the means and the budget available for this production, the results are amazing. Corman switched from "very little money in my budget" to "no money whatsoever". Despite the limitations, the film is quite atmospheric and there is some gothic poetry around it, helped by the casting of the always suave Boris Karloff and the stunningly beautiful Sandra Knight. Jack Nicholson goes through the motions (but his dialogue is totally inept) and if you watch the credits carefully you will notice a young Francis Coppola as Associate Producer.
Despite the "atmosphere" though, the plot is a complete non-sense and, very quickly (i.e, from the moment Nicholson enters Karloff's castle), absolutely nothing comprehensible happens.
The plot becomes contrived and, by the end, you're not too sure as to who is who and is doing what. You're not too sure if Jack Nicholson is staying or is leaving and actually you start wondering why you started watching in the first place.
However, for many movie students, "The Terror" has to rank as one of the most spectacular examples as to how someone can make a movie with absolutely no resource whatsoever. Respect, but this does not make "The Terror" a good movie...just watchable, and certainly not at the level of the Poe cycle that Roger Corman was filming at the same time.