Catacombs of Knoss was as amazing as ever now that I played it second time! I have to say that I can't remember all the details since it has been a couple of years since my first playthrough and that's why it's hard to say what's new and what isn't. I believe Part 1 had some new areas/buildings to explore. They fitted in very well and made it more interesting to explore.
Part 1 is a very good Thief Gold city mission that has a nice layout and good climbing opportunities around the city. Still, as good as the first part is, for me Part 2 is really what makes Catacombs of Knoss so spectacular! Part 2 reminds of Down in a Bonehoard but still it has so much unique areas to explore that make it interesting!
Lastly, a couple of most memorable moments for me: hovering lanterns (they add so much to overall atmosphere), petrified wizards in the midst of battle (one of the coolest things I've seen in a FM).