An enjoyable tale, but not especially brilliant. I must admit, my attention wandered sometime around the point the Solarians showed up. I quite liked the aliens in this one--as soon as they stopped reminding me of Gollum in the Lord of the Rings. An unfortunate bit of voice acting, there.
Charley's rant to the Doctor regarding his penchant for martyrdom was particularly well done, and spot on. The Doctor (whichever incarnation) has always had a tendency toward grand gestures and melodrama. It's nice to see Charley poke a hole in Eight's fatalism.
I'm giving this three stars because I couldn't help wanting more.
A greater depth to the story and characters. Big Finish at its best can really knock it out of the park. Embrace the Darkness was a good, solid effort, but not a particularly memorable one.