I've seen the whole lot, and I have to say it has its ups and downs. Its a tad predictable, mainly because Arthurian Legend has been done to death, and Eva Green's voice can be quite annoying at times. But the variations, like the forthcoming episode Lady of the Lake
where the myth is turned on its head showing the daughter of the swordsmith, a girl called Excalibur, who was drowned when Merlin looses control of his power and freezes the lake with her in the water, leaving her hand, and the sword sticking out.
which shows how history can be rewritten, really give this show something new and interesting that kept me watching. Also, Jamie Campbell Bower's performance and transformation of this morally ambiguous womanising teenager pushed into kinghood and developing into the beginnings of a great king is truly a great watch.
It is far superior to the BBC's Merlin, they have at least tried to stick to the actual mythology, instead of making most of it up.