One of the first games I picked up for my Wii, was Resident Evil IV.
Yeah, it's a little gruesome - lot's of creatures, lot's of guns/weapons, lot's of blood. Given the mutant/monster theme, it's not something I find particularly offensive, but it's not the first game I'd pop in if I had kids. But for folks who like shooting things, it's a blast.
Unlike the crazy stuff kids play these days, it's simple enough for occasional players to figure out quickly, with ever increasing skill required to progress. Good strategy becomes imperative the farther you get with it - being good on the trigger, and having the right weapon isn't enough. Very, very addicting...makes good use of the unique Wii controllers as well.
Another option I'd highly recommend - a charge station. There are a few out there now, but I've got the Nyko -
Amazon link here. While alkalines in the stock controllers last quite a while, converting to rechargeables is cheap and avoids the battery swap hassle.