My still reigning co-op favorite shooter Rainbow Six Vegas 2 has come under fire this holiday weekend due to an unexpected - and unpleasant - surprise. It turns out that Vegas 2 and other titles featured on Xbox Live's Games on Demand service may or may not be compatible with their disc-based brothers. The worst part? There's no way to tell without buying and trying...and if your gamble doesn't pay off, Microsoft still will not give you a refund nor credit.
In addition to Vegas 2 woes outlined in the article, LEGO Rock Band is getting a bad stigma in the comments section due to the lack of song export code that would normally be provided with the game if it was purchased on disc. These are serious oversights from Microsoft and these respective publishers Ubisoft and EA. After the dust settles and you're looking to spend that spare gift cash, be sure to do your research before buying a Games on Demand title.
Source: Crunchgear.com