+ Amazing new artstyle, UI and overall graphics!
+ Story and lore, with lots of cool flavor text.
+ Evilopedia with lots of information about enemies, buildings etc.
+ Pop-up tutorials, and information about new buildings and enemies.
+ Fun new gameplay elements like seizing various buildings, and collecting randomly dropped items.
+ Very creative and fun "Night Mode".
+ A lot more polished gameplay than already great CT1, and overall a lot more fun! :)
+ Great sense of progression with new and improved skill tree.
+ A lot of Badges and Newgrounds Medals to earn.
None, I can't really think of any!
I've already said that personally I felt like Cursed Treasure 1 was one of the best tower defense games, but with Cursed Treasure 2 there's no doubt that objectively it's one of the best tower defense games of all time! I highly recommend playing it.
I hope you guys will keep expanding the franchise. :)