This is quite fantastic, isn't it? One of very, very few (six in total, though the DW restoration team did a fantastic job with animation to complete the epic 8-part serial "The Invasion", effectively making it 7) fully surviving Doctor Who stories from the Second Doctor's (Patrick Troughton) era, and boy is it good. No, it's not absolutely perfect, but who cares if it's a bit padded, when this one is thrilling, it's thrilling.
I consider myself a huge Doctor Who fan, but I must admit to drastically preferring 70's and even to an extent 80's Doctor Who over 60's Who. From what I've read of Target novelizations and from the reconstructions I've seen it doesn't really appear that the Second Doctor's era was consistently great, but the evidence to the contrary is overwhelming. First we have the surviving stories (all of which excluding "The Krotons" are rather excellent), then we have a couple of stories which have reconstructions that rival in riveting thrills some of the best Who stories. So maybe it's more accurate to say I generally am not fond of Hartnell's era (though it too has its fair share of hits). Anyway, the point I'm getting at is that even for someone who doesn't like the pacing and feel of 60's Who this is great entertainment.
I think that the fluid visuals help keep this story alive. It's very well filmed (well, videotaped) and there's actually some very interesting video editing used as special effects (which by the way look great by Who standards in this serial other than the monster costumes). It's a welcome change from the frequently static feel of early Who. The direction is very good, both in terms of visuals and dramatic elements as the performances are excellent all around. The script by Brian Hayles is very good and provides ample room for excellent interaction between the Doctor and two of his best companions, Zoe and Jamie. Oh, and this one has a good number of scares too!
9/10