Was just about to come in here and start a topic on this. Absolutely phenomenal show. Easily the best new show of the year and probably the best since Homeland debuted. Matthew Rhys, a Welshman btw, is ridiculously good in this show.
I think the FBI agent as neighbor device serves as a great parallel between the two families. Not too big on it in terms of tension which is kinda cliched, but overall I think it serves a strong purpose.
Can't recommend this show highly enough. If you like Homeland, Mad Men, Breaking Bad, etc. you will most likely love this show.