Not bad for a first attempt. Firework shots by themselves, although colorful and bright, can get repetitive and aren't all that stunning to look at. Including something in the photo such as a cityscape can dramatically add to the overall shot. I find it much easier to shoot wide to include the surrounding skyline, that way you should be able to get each burst in the frame without having to move your camera's position. Although you may not get to attempt these again for a while, start out with a low iso, f/8-f/11 and bulb mode. Make sure you have a sturdy tripod and a cable release/wireless remote also. Keep shooting!