It's the same with any serial though fantasy or otherwise - there's only so many situations to explore - like the last Robin Hood *spits at memory* always having to find an excuse to go into Nottingham
or the A Team always getting locked up with power tools at their disposal etc etc
Actually what I did like about this series was how they managed to weave a lot the major canon for the Arthurian legends (aside from the obvious palsy walsy same age Merlin & Arthur) back into loose sync without involving christianity in any way
Also Emilia Fox as Morgause - she even managed to make Katie McGrath look good and do something more than the eye candy thing
Seen the first 3 episodes of season 3, and I absolutely love'em!
But it was great. I'm just soooo addicted now, I don't know what I'll do until the next season comes out. 