Hi,
Certain trains in Germany and Austria still have compartments, 3 seats across facing each other. They have been electronically adapted to any electronic gear you might have. Other than that, these trains (IC) basically look like they did 40 years ago, except refurbished. Yes, you could be sitting 6 hours or more facing someone doing the same to you. Germans tend to stare much more than Americans and, I would also say, than other Europeans. Sitting with amongst complete strangers is the European way of train travel, sometimes it takes almost 10 hrs or so depending where you're going, such as Krakow to Berlin.
"...trains had seats just like a plane." That sounds like in Germany the ICE where it's general seating, sometimes sharing a table with 2 passengers in front of you.
In Germany you can still hop on with your Pass without a reservation. If you see no seats available, you either stand and wait for a seat or you move to the next coach in search for seat. People do this all the time, esp on regional trains. Reservations are not sold for regional trains in France, Germany, Austria. It's first come first served, same as in Poland. I find train traveling in Central and Eastern Europe a lot less restrictive than in the West such Belgium and France as regards to flexibility, hopping on. mandatory reservations or none,