Don't think the sales problem with this game is majoritarian "on-rails" issue. It could account for some problems but I'll give you a hell of a lot better reasons:
1. Overshadowed by the much bigger release that was New Super Mario Bros Wii.
2. Probably losing a lot of potential sales to Cabela's considering this is going to be seen as a light gun kinda game.
3. Marketing compared to the first one has not been as competent and pervasive. Although hype machine was working for it during the summer, it died away in the coming months to its release and little advertising before and after its release.
4. Finally it's a spiritual sequel to a game that wasn't that highly praised and potentially bought for the RE brand rather than a solid game.
Those reasons seem to be a more logical assessment of why Darkside Chronicles is failing to hit with the Wii audience right now. You can throw in the on-rails part as well.
