This is really aimed at the lighter side of the CIA/Spy theme/plot, rather than the harder edged conspiracy series. Whilst it's not a comedy Covert Affairs is the kind of programme you put on when you don't want to get too bogged down in a beefy complicated plot. Though you will have to pay attention to some of the story lines.
Piper Perabo fits into the role of Annie Walker, the new field recruit for the CIA. But she has a decent supporting cast including a good performance by Christopher Gorham who play the role of "Auggie" the blind operative who mentors Annie and provides operational support. It's not easy to play a blind person convincingly and he does this very well.
Other cast members are also quite comfortable, Kari Matchett and Anne Dudek fit into the boss and sister roles for the most part successfully. Early episodes do tend to overplay the sister/sister relationship and strains a bit more than I expected (this does ease off later on in the series and in season 2)
I would tend to agree that the effects in some episodes, including the "green screen" work isn't top tier (but it does the job). Story wise I found it quite easy to follow and in most episodes a good watch. But this isn't the type of series everyone will warm to, though I find it easy watching. It won't really be your cup of tea if you like a gritty more realistic type production, and the stories can be a little unlikely and stretching reality a bit (though this is hardly rare for this genre) Piper does lift the series with her performance with some good acting and portraying the career minded woman keen to impress, but also a more vulnerable personal side too. Worth a look if you want a spy "lite" series to watch as and when you please.