The Curse of Fenric is regarded as one of - if not the - seminal McCoy story. It is part of the Ace crescendo, a key part of the so-called "Cartmel Masterplan" and features some of the best plotting of any post-Bidmead script. It's also part of the thrum that led to such a successful Original Series sendoff, which climaxed so pleasingly with Survival (and created the Virgin New Adventures). It's a little contrived at points, but we're talking about Doctor Who here, so that's forgiveable. The biggest question mark on the whole "masterplan" - apart from whether it actually existed, if you do some reading - is why the Doctor feels the need to only reveal the plot in small morsels even though he apparently knows what's going on from the very beginning. There's no real reason for it, and at times makes this incarnation quite frustrating.
The acting is relatively tight (except for Eastenders rejects serving as vampyrettes), with all of Millington, Rev. Wainwright, Judson and Kathleen Dudman being portrayed convincingly. It is much more striking for the simple fact that's it's backed by quality production values - SFX, animatronics (?) and masks.
Thinking outside the box. Perhaps Ian Briggs' most impressive feature in this script is his lateral thinking skills. The "chess" motif is done to death in nearly every media, but it's utilised well here - as is faith being the only defence against haemovores. It is, however, unsurprising that there is an underlying pessimism about humanity's future given the serial was commissioned and edited by Andrew Cartmel (whose book Warlock) I found amongst the best of the Virgin New Adventures.
Even though the Cartmel Masterplan - and the Script Editor has implied he spent three years obsessed with Sophie Aldred - was discussed in point one, Ace's attempted-sexy "There's a storm coming" sequence is just embarrassing, for the writer and actor. I don't care if it's part of the "coming of age" story arc, it's about as erotic as a wet fart and sounds only marginally better.
In a word: Crescendo.