Susan C.
Yelp
Potsdamer Platz is one of those places you can't miss simply because it's in a fairly central area--if you are into cultural and artistic activities such as museums, memorials, concerts, shopping (like how I threw shopping in there ;) you'll probably catch transportation close by. You'll likely stumble upon this plaza if you're visiting and your hotel is near, or if you're walking between attractions, or simply commuting and transferring between different trains.
It's maintained its role as a transit hub since the mid-1800s, when it was the location for a long distance train station. After WWI, Europe's first traffic light was installed at this intersection. The square was destroyed in WWII and subsequently became an area for black market activities where the purviews of the foreign powers coalesced, and further became a demarcation between East and West Berlin when the wall went up in 1961. The area was devoid of infrastructure development until the 1990's once the wall came down, followed by major corporations moving in, and new buildings and highrises going up expeditiously to accommodate the needs for commercialization.
While I didn't see anything exciting happening in the area when I was there, other reviews mention a Christmas market and other holiday, performance and community events being staged here. Surrounding the square are a number of retailers including the Mall of Berlin, some restaurants, and a lot of office buildings.