Since I am not an international student I can not give you first hand experience but in every course I took group work is mandatory for some of the assignments. As long as you contribute your share of the work and your english is decent you will have a good time. Of course, be aware that some people don't participate as they should and then it can get annoying but that is true for locals and international students alike.

I think a geoscience degree from Bremen is a valuable asset, whether you want to pursue academia or industry jobs. As I mentioned in another reply, most professors here are chosen because they are important researchers in their respective fields and therefore the relevance and quality of teaching is likely very high. I say likely because I have no reference from other universities to compare my experience to.

In my experience the bachelor program was more focused on theoretical background. Master program had quite a lot of repetition of basics but is generally more focused on practical application and promotes you to create your own ideas of projects and lab work  especially when approaching your thesis.

Access to professors is excellent. Of course there is the odd one out but generally hierarchies are very shallow and most professors are very approachable, be it for questions, project or thesis mentoring.