The burgers I have tried have been alright, but I did not find them very filling. I also had avocado toast that I honestly thought was terrible.
My feelings about the food I have tried in Germany have been very mixed. Some foods surprised me in a good way, like the burgers that were better than I expected. Other foods were very different from what I expected. Mayo here has a vastly different taste than mayo back home. Usually I feel the food is not as good as I had been led to believe, but regardless I get excited at the thought of trying the food. It's a unique experience and broadens my understanding of German culture.
Speaking of experiences, one funny experience I had was with spicy sauce at a Doner shop. Germans generally do not eat spicy food, so I asked for the really spicy sauce. The shop owners actually kept this sauce hidden underneath the counter because so few people ask for it. One time, I asked for so much of it that the owners thought I would not be able to handle the heat. They were laughing and waiting to see my reaction. However, when I finally tried it, I found it only mildly spicy. They were quite shocked that I could handle it so easily.
One of my funniest food disappointments happened when I ordered fries with cheese. I imagined getting fries covered in melted, gooey cheese, but instead I received unmelted strands of cheese sitting on top of the fries. I was very confused. I also noticed that the cheese sold in German stores has a much stronger flavor than the cheese I am used to eating. These experiences made me realize that even foods that seem familiar can be prepared and eaten very differently in another country.