There's definitely room for a spin-off there. You know, with Arthur yelling about saving the United Kingdom last week and the dragon promising Arthur would return at a time of great need ... If I were Alex Salmond I'd be a bit worried right now.
I liked the ending at Avalon. I've spent the last 3-4 weeks hoping they wouldn't follow the legend and kill Arthur off, but in the end I like the way they did it, especially with getting the magic secret out but doing it in the last 45 minutes of the whole story so that it never changed the whole dynamic of the show or Merlin's relationship with Arthur.