Word of Amazon's offer comes a day after Walmart.com began enticing Halo: Reach (Xbox 360) and Super Mario Galaxy (Wii) pre-orders with a $20 e-gift card.
But while the offers seem similar, there are some significant differences. Those that pre-order from Amazon will receive their credit "within 2 business days after the product ships," while those that pre-order from Walmart get their credit immediately. Furthermore, Amazon's credit is only applicable towards a future video game purchase, whereas Walmart's can be used on anything that the online marketplace has to offer.
On the flip side, Amazon has a good track record for delivering games on release day, something I can't necessarily say about Walmart.com as I've never ordered from there. Either way, regardless of the retailer, it's still a good deal--you're getting a third of the game's cost back, after all. Thanks to Shacker rrmills for the heads up.