The original 'Dawn of the Dead' was the middle movie of 3.
Night of the Living Dead
Dawn of the Dead
Day of the Dead
'Night' was a great movie - originally made in B/W, then re-made in colour (by the same director) - the B/W version was more atmospheric, and more scary
'Dawn' originally only had 4 main characters holed up in the shopping centre, so the relationships between characters worked better, you cared more about each character, and so, got more involved in the plot.
Obviously, being newer, special effects are better in the 2004 version, but again, the original was more atmospheric, and the 'tense' moments were more exciting.
'Day' - IMO, was a shameless gore-soaked cash-in on the first two - I hope to God they don't remake that, as the original was poor enough to start with.