I know it is an extremely popular event and I feel very lucky because with my first try I won the ballot. I bought the VIP package which included massage services an extra T-shirt etc. The course is flat and the temperature was perfect with light rain and around 10-12C degrees. Of course, it was very crowded with 30K+ participants which help you, on the one hand, keep a high pace but on the other hand bit challenging to by-pass others if you want to run faster. The goal is just after passing the Gorgeous Brandenburg Gate which just amplifies your emotions. I will highly recommend Berlin marathon which I like this city so much.