I'm baffled by the critism of The Hornet's Nest from some online commentators. Of course it's not like a Big Finish audio play, this is because it isn't a Big Finish audio play. Of course it's not like a Fourth Doctor television story, but it isn't a television story. I admit that Tom Baker is playing Tom Baker even more obviously than he did on screen in the 1970s; it's also true that this is the Doctor presented as earthbound paranormal investigator rather than traveller through all of space and time; but it seems to me entirely within the range of the Doctor we know (especially as supplemented by Baker's performance of himself as late). It's not blow-me-away brilliant, but very entertaining.
The Robots of Death was one of the best Fourth Doctor stories, and its writer Chris Boucher brought the Doctor and Leela back to the same planet in his novel Corpse Marker. Alan Stevens and Fiona Moore, who had already gained my respect for their activites as critics, together with Boucher and others, generated seven audio plays based around the interactions between Commander Uvanov (now running the planet) and the mysterious Kaston Iago (played by Paul "Avon" Darrow, though I think they are different characters), fighting off the cultists of Taren Capel and also facing up to another Fourth Doctor era monster. The first five plays form a pretty decent story arc, of which the first is unfortunately the weakest, but the others all enjoyable. As well as Darrow, Russell Hunter reprises Uvanov and other characters are played by Peter "Nyder" Miles and Peter "Zen" Tuddenham. The sixth play, "The Prisoner", is a much shorter face-off between Darrow and Miles, in their characters from Kaldor City but effectively as Number Six and Number Two, very nicely done. The last of the plays, actually set on a storm miner, is rather detached from the others and can be skipped (though you will probably want to listen to it anyway).
I have also been listening to the ongoing series of Bernice Summerfield audios from Big Finish, though I have not been writing them up as I go (likewise the Dalek Empire and Cyberman series). There was a sequence of three particularly good ones in the middle of Season Seven, however, which I wanted to note here: Timeless Passages, by Daniel O'Mahony, which involves a time-shifting library; The Worst Thing In The World, by Dave Stone, which is set on a Hollywood-like planet where different genres of entertainment are getting lethally entangled; and Summer of Love, by Simon Guerrier, in which the entire population of the Braxiatel collection appears to have become sex-mad. All very entertaining.
There is of course only one science fiction audio play that anyone has ever heard of, and that is Orson Welles' 1938 adaptation of H.G. Wells' The War of the Worlds. I was delighted to find it downloadable from here. Anyone with the slightest interest in Wells, Welles or audio sf plays needs to hear it. It is only loosely based on the original novel; the brilliant introduction is retained, but then we are into light music interrupted by increasingly desperate news bulletins and horrible events, culminating with Times Square and the rest of New York succumbing to poison gas. That takes us to the 40-minute mark, at which point we are reminded that this is a work of fiction; and then the last third is essentially a post-holocaust survival story, Welles' Martians having been much more thorough in their devastation than Wells' originals. And at the very end, Welles himself steps out of character to remind everyone that it is Halloween. The discerning listener will have had no difficulty working out that it was fictional even if they tuned in after the first two minutes, but of course not every listener has the time to be discerning; my own adopted country was convulsed for days after a deliberate media hoax three years ago, so I can believe both that there was a significant public reaction to Welles' broadcast, and also that it makes an even better story if exaggerated. Anyway, it's essential material for any sf enthusiast.