Just finished Inferno.
I'd say this was definitely my favourite Pertwee story so far. When he first started looking around after using the TARDIS console, I thought he'd maybe travelled to the future and would see what was to come, then would go back and change it. But then BAM, parallel universe story!
Again I got a strong feeling Star Trek TOS may have had an influence here. The parallel universe full of evil counterparts, facial scars, and inverted facial hair just screamed "Mirror, Mirror", which would have been recent in people's minds. That's not a bad thing, scifi has had so many different takes on these classic ideas, and so many scifi shows have been inspired by original Trek in particular. The eye patch was a nice touch of cheese.
Doctor Who has had some parallel universes episodes in the modern series, but it's been kept as a fairly difficult and rare occurrence, so this one was a pleasant surprise. I'm not sure if it's something they do again in the classic series.
Overall a really good story. I love the messing around with tech, so I was happy to finally see the TARDIS console make an appearance, and be a pivotal part of the story. It had elements of a typical Doctor Who plot, with the advanced sciencey operation, led by some a-hole leader who won't listen to reason (Fury from the Deep, anyone?), but then added the new element of the parallel universe to get around some of the limitations of being Earth bound and add some twists.
My only problem with the story was those awful and unnecessary generic werewolf monsters. What the hell was that about? Beyond their initial discovery of the goo, they didn't really deal much with the fact that there was green goo inside the earth that seemed to infect people with contagious werewolf syndrome, and it was unnecessary since it already had the danger element of DESTROYING THE ENTIRE PLANET!
The monsters weren't really brought up much again in terms of plot either. It was just oh shit, monsters being monstery. They didn't care much about where they came from or what they were or how stopping the drilling would also stop the monsters, because you know, Earth being destroyed and all. The story had monsters for the sake of it, they weren't the story.
I'm looking forward to starting the next season.
edit: Ok, I'm two minutes into the next episode and my excitement level has already ramped up to peeing my pants.