Okay, I feel like you have to judge this show with a grain of salt. I've actually found it very enjoyable and oddly addictive, though that doesn't mean I think it's good. Yes, there are plot holes, character inconsistencies, cheesy dialogue, etc., but I think because it doesn't take itself too seriously (like, for example, Robin Hood was prone to do) it can get away with most of these things. There are moments of genuine comedy that I really appreciate, and the rest of the time I spend giggling at the aforementioned flaws. I think the cast is quite good as well: Colin Morgan is charmingly dorky as the title character; Anthony Head milks a surprising amount of emotion from a ridiculously poorly written character; and the rest (except perhaps for Katie McGrath, who can be a little too emotional) imbue their roles with genuine humanity. I especially like the growing relationship between Merlin and Arthur-- the way the show is written, Merlin's only reason for helping Arthur is that 'it's his destiny,' and Arthur has no real reason at all to help Merlin, and yet you definitely feel that they are starting to care for each other.
So, yeah, it's no television masterpiece, but it is fun to watch, and sometimes that's all you need.
So, yeah, it's no television masterpiece, but it is fun to watch, and sometimes that's all you need.