I don't think anybody is sure how well lightgun games do in Japan, mostly because there have been so few over the last few years. One of the reasons Umbrella Chronicles is (probably) doing so well is (probably) that it's the first proper game of the genre to hit the Wii, and I've heard lots of people say they'll buy the first lightgun game to come out. On top of that it looks like it's pretty decent (had 80+ on Metacritic before GameSpot...), and has huge fan service appeal to fans of the Resident Evil franchise.
I wouldn't call it a casual game though. Casual to me means a game is less about skill (ie. you don't have to learn how to play it) and accomplishment (ie. rarely a campaign that you beat), and more about being easy to access, fun in small amounts, and so forth. I guess anyone could pick this game up and know what to do (aim for the head!), but calling it casual feels very wrong to me.







