Not perfect. Certainly a British point of view on spy thrillers, which are normally more thoughtful, better written, and better acted than US drivel, such as the current version of Nikita or 24.
The characters were human and entertaining as individuals. They developed as individuals. The plot is a little convoluted but eventually you figure it out. There are no 180 degree twists to keep the plot going, just the gradual discovery of new information.
The acting was British but not to over the top. There were a few too many altercations that didn't result in damage whose effects disappeared too fast. They spent a lot of time setting up the next series, so it would be a shame not to see some of it at least.