I had an absolutely amazing time for my SDE internship at Amazon in summer 2016. My mentor and manager were both really great at making me enjoy my time there and getting me to work better - I had daily talks with my mentor as well as weekly one-on-ones with my manager.
Interns typically get to work on their own project over the summer, which they present to other teams at the end of the term. You're expected to take a lot of ownership over your project during the time, so you get to make a lot of the decisions when it comes to your design and deliverables.
My project was scoped out well, so that I knew what I had to do at what time. The project was fun and challenging while still manageable.
There's a lot of other interns around and weekly events - so that part was also fun.
I chose to take the housing stipend for $2500 / month.