I agree about the Microsoft Points system. I knew I only wanted Operation Anchorage and Broken Steel and that I would need 1600 points to purchase both. I discovered I could buy Microsoft Points at the Zune Marketplace
in 400 point increments instead of the 500 point increments listed on the Xbox Live website. I'm pleased to report that I do not have any Microsoft Points left on my account.
Perhaps I'm posting this too late for D3
but I share this in the hope that it will help someone avoid having an unwanted Microsoft Points balance.
At this point I plan on waiting for the GOTY edition of Fallout 3 in October so I can have access to all Fallout 3 DLC and avoid purchasing through GFWL.