Jersey Shore is far and away the most iconic tv show of the past 5 years.
American Idol for the past 15 years.
Desperate Housewives is also very iconic, though, as is Lost. MF and TBBT are hugely popular but iunno if iconic is the word. They are the top comedies but they're not the #1/2 shows overall like true iconic sitcoms (Seinfeld/Friends) reigned.
The recent HBO/AMC/Shotime phenomenon is very interesting to me. It kind of represents the Internet age because not that many people have those channels but everyone watches these shows. They completely dominate social media and even regular press. TWD, BB, TB, SoA, and GOT are all iconic shows in a different sense because they represent this shift in viewing. The big 4 networks are hardly powerhouses anymore because of all these shows.
