The RWTH is one of nine technical universities that are part of the “excellence initiative” of German universities. In the engineering and science fields, a wide variety of classes and courses are offered. Most departments have good ties to the industry and many famous companies such as Amazon, Google or Ford have branches in Aachen that cooperate closely with the university. Supervision and support from the staff is good once you get into higher-level, specialized classes. In the introductory, mandatory classes, the number of students is often way too high for the staff to provide individual supervision. It can be hard to find a place to stay in Aachen. If you want to get into the student dormitories, you should sign up for the waiting lists about a year prior to your arrival. Students make up for a large part of the city’s population and the university offers many different sports courses, so it’s easy to meet people and find activities for your free time.

RWTH Aachen University has an excellent reputation for their studies, but it requires a lot of self-discipline to even pass exams which are held in German. I am a local student who is studying engineering and I have a lot of contact with Erasmus and international students. During our exam phase (which lasts 2 months at the end of the semester) students are almost only focused on studying, as they want to pass the exams and they often underestimate the difficulty of the course.

This following is based on what I experienced 5-10 years ago: The RWTH focusses rather on teaching theoretical foundations (of mathematical nature in particular) than on practical skills you might need in the industry. There are a couple of practical courses (e.g. for programming) but they are mostly in the form of straightforward textbook exercises.
The bachelor and master courses differ dramatically: There are hundreds of students in the bachelor lectures whereas some master courses are held for only around 20 students. The exams in the master courses are mainly in oral form which allows the examiner to verify the student’s real understanding of a topic. Actually, I see the major drawback of the RWTH in some bachelor courses/exams which aim at mere memorizing and training of mindless routines. However, once you have made it through the basic courses, you are rewarded by more interesting lectures and a greater number of options to choose. I personally liked the master lectures in computer science most cause they really conveyed a sound understanding.
Generally, the teaching system strongly relies on the students’ personal responsibility. For example, the lecturers usually don’t care if you attend the lectures or not.
Aachen as such is an old and beautiful city. It is big enough to have a student-friendly nightlife but on the other hand small enough so that you’ll find calmer areas and parks. The price level (accommodation, food etc.) is generally pretty affordable for students.