The fireworks were fake? 
The footprint fireworks that led towards the stadium during the opening were fired in real life, but the image that was actually show to the world was pure CGI, and was worked on for about a year.
All the money they spent on the show gave us...
* A stadium that only looks good for a distance.
* Faked helicopter cam fly-by footage.
* A few guys goosestepping in with their flag.
* A cute 9 y/o sent out to mime for a 7 y/o that won a national competition to do it, but was deemed too ugly at the last second.
* A blue screen during the torch lighting.