Curse of Fenric is my all-time favourite, along with Pertwee's Spearhead From Space. Being born a generation too late, the only Whos I caught on telly while still young enough for them to have the desired effect were the McCoy ones, barring later repeats.
It's fair to say that Fenric really fucked me up at the time - the images of the sea-demons(?) lumbering onto a bleak Yorkshire beach and stumbling through the graveyard, the vampire girls enticing ill-fated soldiers into the water, the green mist(?) snaking its way through the WWII base and killing every occupant... really bloody creepy stuff.
Yes, pretty bad effects, but it worked because it was all played so deadly straight, without the sort of smug post-modern remarks or Buffy-style one-liners you'd get these days to deflate the atmosphere. The cast were acting alongside men wrapped in bubble-wrap, but my god did they make you believe they were evil mutants!
Fenric is what I refer people to when they say what a bad doctor McCoy was. If only he'd had one more season, I think we'd have seen some really rather stunning stuff...