Why do you guys use spoiler tags? It's an impression topic, why would someone come here if it's not to "spoil" the game a little?
Best question of the day.
The marines have tons of lines, Bungie wasn't overestimating, I just reloaded a level a couple times over to see if the lines changed and they did. Keeping them alive is more rewarding this time, because they are better in a fight and more entertaining.