As a creative type my interview was more portfolio based rather than Q and A, over my career as a student the saw my growth and something about my progress interested them enough to give me an internship. The process is incredible relaxed, helpful, and comforting at the same time, over my schooling career I've had a total of three portfolio reviews.

Took exactly 3 months, declined two job offers from other companies while under GM's process. Not something I'd recommend to anyone who just got out of college, but I felt the risk was worth it and I had a good chance. Applied via online after collaborating on an assignment with employees. They shot an email, then preliminary phone interview, then in-person interview scheduling, fly you over if need be, then waiting until an answer. Each step usually took exactly a month (initial interview -> in-person -> answer). There's a lot going on inside the tech center right now and a lot of passing your application around like a hot potato. This is normal. Don't get frustrated, be patient, be grateful, be nice. Every interaction with GM employees has been absolutely positive, I feel the company is headed in a very positive direction and they do pay well. If you've caught their attention, don't take it for granted. Someone here said that usually the longer it takes, the slimmer your chances. This might apply to other departments, but GM is BIG. If you snooze or give up, you might lose a fantastic offer and the chance of a lifetime if you're starting your career and want to settle down. They do use STAR format. In-person interview has portfolio and questions portion. Questions portion was with two managers and they only asked 4 questions, portfolio was in a conference with 5ish people and you present your work while they ask. Just be prepared, practice, look through glassdoor for questions they may ask you, and be presentable. This isn't just anyone looking at your work. Overall, positive experience.