The Diplomat begins with an ambassadorship to the UK amidst an international incident where a UK vessel has been attacked in the Middle East. What ensues is a scramble to figure out the culprit while taking into regard the concerns and positions of all parties involved.
Having been around diplomats before, I think this show does a decent job trying to show the grit of overt espionage that is diplomacy... namely intense negotiating (mostly overtly but sometimes covertly), reneging positions (including backroom deals, walking back promises)... and especially that important policies are sometimes at the mercy of the personalities of the people involved (including egotistical, petty, flustered diplomats or politicians).
I also worry that the majority of viewers may not have an international relations background for the fast-moving dialogue and all the intricacies alluded to. Especially in today's world, one country is seen simplistically as a friend or foe, but in reality, like the show portrays, each country is made up of a web of partisans each agreeing or disagreeing with different policies their country takes (hence why spies are still able to share info covertly with overtly antagonistic countries).
Finally, I think the show does introduce certain personal relationship dynamics (romance) to cut through the diplomatic dealings so that the lay person (who tends to be more gossipy), can follow a romantic drama or two from the show.
I do enjoy the show, first for the mystery element to figure out who attacked the UK vessel. Second for the multitasking of tapping sources to out things in motion, hence I like Hal (Rufus Sewell's character) the best. Third, I like to see the dynamics that allies do have tension (US-UK, UK-France) while foes do have back channels (Iran, Russia). Personally, I don't care much for the romantic relationships because if you are in service for your country, personal relations should take a back seat, I feel. But again, I think it's there as an element to pitch the show to a wider audience.
I am excited to see subsequent seasons.