I started playing the expansion last night. It's such a weird feeling - playing Destiny and having so much to do I didn't know where to start. The new quest interface is brilliant, the game has been crying out for something like this.
From what I've played of the story missions so far they seem miles ahead of OG Destiny. I know what I'm doing and why I'm doing it. Also, cutscenes! Decent ones. Involving the various characters from the Tower that until now, have just been vendors. The world is starting to feel alive.
Where as 1 year ago Destiny was a great playing game with an extremely odd, "unfinished" feel to it, TTK feels complete. It's a real solid foundation for the next year of Destiny and I think it's going to finally live up to all the pre-release hype.