This audio had all the markings of something I wasn't going to enjoy.  It is a script by Nicholas Briggs, which usually means it is a story I'm either going to really love or really hate.  It's part of the Dalek Empire storyline which in general I haven't connected with much at all.  In fact, The Mutant Phase is the only chapter of that loose arc I've actually very much enjoyed so far.  And it is generally not very well liked among the fan community.

Yet I found myself enjoying every part of The Mutant Phase and happily following along through the adventure.  It felt like a story that very much kept the Fifth Doctor and Nyssa active and engaged with the events at hand.  I really liked how the Daleks reacted from this genetic disease of sorts spreading through them.  I thought it was well done and fun how they were panicking about this but not really willing to seek out help, either.  We don't often see these villains on the back foot like this - at a distinct disadvantage and in a fairly weak position.  It was very well done on the whole, leaving it the strongest aspect of the audio.

I mostly liked how it was all resolved through a paradox, to a degree, although that part is also where Mutant Phase is at its weakest - being an entertaining enough novelty while also being a little overblown and this still being early for Big Finish to rely this much on sound effects in resolving the plot.  Still, I did enjoy it, and would definitely recommend The Mutant Phase.