I enjoyed the first 7 or so episodes - entertaining, and most importantly FUN to watch. A nice break from the 'ever so gritty' style of more or less every other action series.
Sure, it's a semi-believable premise if you analyse it, but the point is not to analyse it. If you analysed James Bond, the whole idea is ludicrous, but it's still great.
Unfortunately, the believably really stretches in episodes 9 and 10. I found my self saying 'what?! that's ridiculous!' on more than one occasion, to the point of cringing. By the end of episode 10 I was playing with my phone instead. They lost me.
The other thing that went missing was the fun. By trying to be 'more gritty' in the later episodes, they lost the point. I'm sick to death of 'gritty TV'. The reason I liked this is because it had humour and warmth in it amongst the explosions and fight scenes. Is nobody else just utterly bored by long humourless fight scenes?
Might watch the next series but only for long enough to see if they've learned their lessons or not.