No idea if you have gone yet, but Goethe Institut are awesome!! !
I did a similar course 2 years ago, a 3 week Intensive course in Berlin with the Goethe Institut.
It was a lot of fun! I did the B1.1 course. I learnt a bit, mainly from talking to the teachers in German, but most of the other students spoke to me in English because their English was better than their German, which was a shame because it meant I was practising my native tongue!
But basically you get as much out of it as you put in. Really try to only speak in German if possible and try to listen and take notes in class. It can be hard because everyone is quite excited to be there and study seems like less of a priority.
But basically it will be an amazing experience that will open you up to a whole new world, you will have a ball of a time, and by the end of the 4 weeks you will feel a lot more comfortable and natural speaking German!
Viel Erfolg!! !
Tschuess.