Of course, a few restrictions apply. For starters, the discounts are only valid on Xbox 360--PC and PlayStation 3 owners are out of luck--and you need to have either bought or redeemed an Xbox Live Gold membership to get the discounted price. Sorry, Silver.
Once you're logged in as Gold, you should see the following prices until March 29:
- Operation: Anchorage - 400 Microsoft Points / $5
- The Pitt - 400 Microsoft Points / $5
- Broken Steel - 400 Microsoft Points / $5
- Point Lookout - 400 Microsoft Points / $5
- Mothership Zeta - 400 Microsoft Points / $5
Now, as for which ones are worth it, I'm partial to Broken Steel and Point Lookout myself--Steel for raising the level cap and opening the world back up after the RPG's ending, Lookout for its sizeable chunk of new land--but that's just one opinion...