A comparison video of Battlefield 3 for Xbox 360 by WikiGamesGuides reveals what kind of difference the HD texture pack makes. Last week, EA finally fessed up to the feature, with executive producer Patrick Bach saying the difference would make the the game look "standard-def." He wasn't kidding -- the difference is staggering.
The pack install is optional because, unlike PCs and PS3, hard drives aren't standard for the Xbox 360. The real question, though, is why does it look this bad without the pack? Even ignoring all other non-EA, DICE games, Battlefield: Bad Company 2 didn't require a hard drive install and still looked fantastic. If you don't have a hard drive for your Xbox 360, consider this a warning.