One thing I found out last year when shooting fireworks is to try not to release the shutter until after the fireworks have gone off. The initial explosion tended to be too bright and part of the picture ended up being overexposed like the first pic posted.
When I first tried fireworks, I was leaving the exposure open too long (like 20+ seconds) and then there was just a mash of explosions that lost definition and impact... see the last picture.
Camera: Pentax K10D
Exposure: 2 sec (2)
Aperture: f/10
Focal Length: 33 mm
ISO Speed: 100
Exposure Bias: 0/10 EV
Camera: Pentax K10D
Exposure: 2 sec (2)
Aperture: f/10
Focal Length: 33 mm
ISO Speed: 100
Camera: Pentax K10D
Exposure: 30 sec (30)
Aperture: f/22
Focal Length: 19 mm
ISO Speed: 100