How it'll work is that every NEW copy of Gears 2 will come with a redemption code to download a free "Flashback" map pack from the XBLM. This free DLC contains five additional Gears 2 multiplayer maps which are (surprise!) remakes of classic Gears maps including Canals, Gridlock, Mansion, Subway, and Tyro Station. This will ultimately bump the total number of GoW2 multiplayer maps up to 15. We're told the Flashback map pack DLC should be available for download on launch day, but note that Epic has no plans to release the maps as paid content. It's their "thank you" present to loyal fans, so be sure to stay clear of those used copies that are code'less.
GamePro also confirmed that anyone attending a Gears 2 midnight launch event will be given a redemption code to unlock the in-game golden Hammerburst (as seen above) which features a gold plated paint scheme similar to the Collector's Edition's golden Lancer.