It felt very "meh" to me. Too long for the content it had, and missing a bunch of stuff. I think it was constrained by CV filming restrictions but instead of managing to write a tight story like the New Year Special which made very effective use of a "bottle" episode and very limited cast, it felt like something which was put together with paper and sealing wax. The lack of a crew on the pirate ship felt like such a cheat. Having her children hostage was fine. Having the whole crew hostage was just stupid. She's supposed to get what the Sea Devil wanted without having any backup whatsoever? That's just stupid. Who sent her on the mission which freed the head Sea Devil, anyway? There were no other Sea Devil speaking parts, but the one in charge had been frozen for centuries...

The characterisation of the Sea Devils was also jarring. Harking back to the Pertwee version but then showing a race completely at odds with that (without even the saving grace of an intra-species difference as they did with the Silurians in The Hungry Earth) just felt sloppy.