Brilliant story! The Doctor is great in this and it's a delight to get to know his new personality a bit better in this story. Zaroff is an excellent villain and gives a convincing and entertaining performance. And the fish people are quite creepy-looking and certainly their predicament is a horrific thought, even if they are a bit silly and trippy in appearance.
As someone who has seen very few Troughton stories prior to the marathon I am currently doing, I do feel like I don't know the personality of the Second Doctor very well, but this story definitely gave me a better idea and understanding of his character. He's cunning, devious, witty and playful. I like it!
I liked this one a lot. Can't really think of anything I didn't like. I'm so glad that half of this story survives in footage, cos if it was all reconstructed I probably wouldn't have enjoyed it. 5 stars from me.