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.