I've been reading the L4D comic for the sacrifice  these past days and I must say I found that there was a good and coherent  narrative that I didn't get by just playing through left 4 dead one. I've always thought that the L4D story was tacked onto the game and didn't sense really  the story coming together. After reading the comic, however I feel that I get better sense of what the survivors are going through and the chronology. I also enjoy the short glimpse into each of the 4 survivor's past.