I didn't know if it was going to be the last or not, but let's say the ending was... conclusive. :'(
I was sceptical of it at first, looked a bit babyish. It was brilliant, however, and I came to look forward to it. Merlin finally went nuclear and whooped some ass, but then it turned out that the big "prophecy" of Arthur's kingdom [SPOILER ALERT] hasn't happened yet... a parting shot of Merlin looking old in the modern day, with a truck going past... waiting for Arthur's kingdom...
So very sad!
EDIT: GW should pay the BBC, because it's wanted me to make a Camelot Bretonnian army!