Microsoft seems to really want people to play The Walking Dead over the holiday break (as they should). Episode 1 is still being offered for free, so as soon as you finish that one, you can jump into Episode 2 for half the price ($2.50). Then rinse and repeat for the following episodes.
Might I suggest buying them all (with your infinite amount of time, money and hope), but not marathoning all of the episodes? That may not be too bad of a decision, as the 50% discount on the episodes is for today only.
{Source: Major Nelson}