The first thing bomb victims experience is the intense flux of photons
from the blast, which releases 70-80% of the bomb's energy. The effects go up to third degree thermal burns and are not a pretty sight. Initial deaths are due to this effect.
The next phenomenon is the supersonic blast front. You see it before you hear it. The pressure front has the effect of blowing away anything in its path.
After the front comes the overpressure phase. It would feel like being underwater a few hundred meters. (At a few thousand meters under the sea, pressurized hulls implode.) The pressure gradually dies off, and there is a negative overpressure phase, with a reversed blast wind. This reversal is due to air rushing back to fill the void left by the explosion.
The air gradually returns to normal atmospheric pressure. At this stage, fires caused by electrical destruction and ignited debris turn the place into a firestorm.
Then come the middle term effects such as keloid formation and retinal blastoma. Genetic or hereditary damage can appear up to forty years after initial irradiation.