I'm not a historian, but a German. So in fact there were two countries, DDR and BRD, or East Germany and West Germany. But in both countries the people were mostly german and spoke german. So there was no big cultural difference, except maybe food. Regarding patriotism: There was just a minority of people who were against a unification of the DDR and the BRD. The people were smart enough to see that the communist part of the world was crumbling and they wanted to be free. After the unification background checks of the administrative elite were executed. So you didn't really have supporters of the old regime in important positions anymore.

I don't know if this answers your questions.

The everyday culture in the two German states was very, very different. This is not only about different television channels - it is a whole culture of childrens songs, radio music, celebrities, children's books etc. etc. that was lost for people in the former GDR. There was a very active movie industry with excellent actors and films, and in their whole worldview very different from the movies that would be produced in western countries. Most of the producers of everyday products stopped producing shortly after reunification - also because their former customers would rather buy shiny west products. The structure of your life was also completely different. East Germans had a fixed workplace and would not be fired, no matter what (of course with the exception of being a bad citizen, something you could easily become f.e. by listening to music not approved by the system). Children would be spending the whole day in infant and then children's care, with both parents working fulltime. Everybody was encouraged to partake in organised activities. There was a more-or-less obligatory youth organisation. And so on. In the West, you had a lot more freedom and would not go to jail for being non-conformist (which was a thing in the GDR).

Having lost all the culture, the products, the tastes of your whole life obviously feels like you are exiled - only in case of the GDR, your neighbors living next door are exiled as well. So no, being completely overtaken by FRG was not a small thing. It really means something that was part of your everyday identity is lost forever.

There are strong bias against people from East and West Germany in the other part of the country. "Ossis" are looked down upon, like a dumb lazy cousin who doesn't know shit. "Wessis" on the other hand are seen as greedy, ruthlessly egotistical bigmouths. People from the other half of the country get identified with the part they are from in a much stronger way, than, say, a person from Hamburg that moves to Munich or vice versa.

The differencies in the cultures formed by different political systems over the years cannot be compared to the differencies of the regions. Of course there will be a difference between Rhineland and Bavaria. But there also is a difference between people from West Berlin and people from East Berlin (although they should be from the same region). This is leveling out a bit, but in Berlin mostly due to the fact that the populations mix up a lot. I suppose that for the whole of Germany, it will take another 50 years at least. In Western Germany, the problem is ignored or its existence is denied (as is often the case with the privileged side) while in parts of the East German population a kind of victim identity is formed, denying their own partaking in the process.

As to your question about building a german identity and patriotism: This is a difficult one, considering German history in the 20th century. Additional you must realize that until the founding of the Kaiserreich in 1871, Germany consisted of lots of more or less small states (that most of the time were struggling with or conspiring against each other). A great part of the 19th century consisted in the effort of creating a German identity. The aforementioned culture of the regions is a consequence of German history - especially when it comes to patriotism or identity, most Germans will gladly identify with and be proud of their region, instead of being patriotistic of Germany as a whole.

West Germany before unification has not been big in open patriotism. After WWII, people had to face the crimes and atrocities of the Nazis (in a lot of cities of West Germany, in 1945 the whole population was obligated to go to the movies and watch the documentations made at liberated concentration camps, with the heaps of corpses and everything). This is also a big subject in school - education tries to make sure there is no way anybody leaves school without a very thorough understanding of the Third Reich and all of its crimes (the classes including obligatory trips to concentration camps). It is difficult to boast patriotism - to be proud of your country - under these circumstances. There always has been a (more silent) patriotism in West Germany, referring to products, engineering, efficiency, culture, and so on - pride of all the things coming from Germany rather than of the country itself.

The GDR on the other hand did have patriotism - based on the idea that all the Nazis had fled to West Germany, more or less (which was not true in the least, obviously). So the Nazis were always "they". This made it very difficult to handle neonazi or racist tendencies in the population (bc the population was not nazi or racist by definition). With reunification, this autodefinition stopped working. I am not sure what if was replaced with - if it has been replaced at all.

I was born in the 60s in West Berlin and have a lot of personal experience, albeit anecdotical. Still I am no historian and will gladly be corrected.