This is one of the creepiest and most gruesome Doctor Who stories of all time. I mean that in the most complimentary sense, though the violence is on occasion too grotesque (I found Condo's death by shooting in particularly bad taste), the gloomy mood of the story, one of the most intense over the show's entire run makes this much more than a silly adventure, elevating it to seriously creepy and effective SF horror. This is one of the most imaginative and interesting takes on the Frankenstein tale I've ever seen, mostly because it ties everything into Doctor Who mythology very effectively.
Comparisons between this era of Doctor Who and the Hammer horror films are common and understandable, but this to me had the air of one of the original Frankenstein films from the 1930's, the feel of a Hammer production as well as a distinctively 'Doctor Who' air about it. This is an excellent production, one of the best the series ever had, I feel. Fantastic and convincing sets, pretty good special effects (though there aren't many in this one), and a convincing and memorable prop used for the actual Brain of Morbius. If you thought Frankenstein's monster was bizarre and freakish, check out this baby, made up of various species from across the galaxies and with a see through plastic head with a brain inside it on top.
The supporting cast are surprisingly not bad at all, especially Philip Madoc as Dr. Solon. Many Doctor Who stories suffer in hindsight from poor acting, but this is not one, and it really helps keep the tension going. The script by Robin Bland (Terrence Dicks heavily script-edited by Robert Holmes) is excellent, with few unnecessary and time wasting moments. I wasn't too crazy about the ape man Condo, or some violence which could've been handled better. I have no problem with violence in Who and in fact find the 2005 continuation of the 63-89 series often too restrained in those terms, but I didn't think it was really warranted in this one, it just comes out of nowhere with Condo being shot with a graphic wound as a result and Morbius in his two versions going around killing a load of people. The script could've handled that better and made it flow properly, but these are minor problems with a real classic and one that thanks to the excellent production and minimal poor special effects is a good one to show the 'not-we's'.
(Oh, and someone release the blasted thing on DVD already, my ancient VHS copy looked fine on my old 20 inch TV but it looks horrid on bigger HD televisions)
9/10