Berliners can be very nice in certain situations, such as the people you work with, but they have a hostile service culture. Not every time, or in every service situation, but you will have enough bad experiences in shops, restaurants and trains to find it annoying, especially if you are accustomed to the more positive service culture in the US, UK and Ireland.
The other problem is that many Berliners regard young foreign workers as being the reason why rents are increasing and this became a political issue a few years ago. I'm not sure what the current situation is but, at that time, you would see graffiti around town, letting you know that you were not welcome, and you would frequently hear the same sentiment expressed in social situations. Ironically, the people who were quickest to let you know that the foreign tech workers were not welcome were the same "anti-fascist" trendies who call everyone else racist.
This hostility wasn't something I experienced when living in other German cities, it seems to be a Berlin-specific phenomenon.