First used to introduce those that purchased Mass Effect 2 on the PS3, Mass Effect 2: Genesis
allowed those players to individualize their experience, by selecting certain pre-game options, in a way similar to those that had the fortune to be able to import their ME1 save file. Later it was promised that Xbox 360 users would be able to download it also. That promise has now been fulfilled. Mass Effect 2: Genesis
is available for download on Xbox Live at the cost of 320 MSP ($4.00).
The 15 minute interactive comic will let players by-pass playing ME1 again if all they want to do is change who they put on the Council or what happened to the rachni queen (along with a handful of other choices). However, you will need a copy of Mass Effect 2 to use it.
I have no real need to buy it as I have Mass Effect 1 and 2 on the 360, but as a ME completionist I feel the need to download it and try it myself.