As far as crowd response goes, Obama (speaking here on the red-carpeted platform, and on TV behind) was the most popular speaker. He gave a 15-minute energetic and inspiring talk. The crowd loves Obama and they let him know
In contrast, they loudly booed their own president (Zuma) every time his image came up on TV, or another speaker mentioned him
The radio here played several times a clip of Obama saying "... and Mandela helped me to be the man that I am now." -- followed immediately by a huge outburst from the crowd, everyone going wild. It's true that that's what happened. But the reason they went wild isn't because of what Obama said -- it's because the technicians in the stadium fixed the TV, and at that very moment Obama's face came onto the Jumbotron for the first time.
Seats up top are full because they are dry! People with the umbrellas are down below, in the constant rain. Admission was free and open, except for those in the box seats in the middle.