The cast are excellent, as are their performances. I've confessed elsewhere in LJ that Anthony Head as Mr. Croup was giving me some minor brain issues, not because he wasn't great in the role ... he is ... but because I've got multiple listens of five series of "Bleak Expectations behind me and he's sorta hardwired into my head as Anthony Head evil role = Mr. Gently Benevolent. I'll just have to listen to "Neverwhere" an equal number of times to balance it out ... that'll work, right? The voice I was actually expecting to sound wrong in the role was Benedict Cumberbatch as Islington; that's because long before Sherlock there was "Cabin Pressure and he's pretty much indelibly imprinted on me as Captain Martin Crieff. But the Cumberbatch surprised me by sounding so much like Peter Capaldi (who played Islington in the TV version) that I actually rechecked the radio show's cast listing thinking I'd missed reading that there'd been an actor substitution.
There's loads of time left to listen to the whole series if you haven't heard it yet!