Normally 3-5 hours a week, and in the rare occasion that a game I'm really (emphasis on this) excited for gets released I end up playing it for three hours a day, which means 21 hours a week. (And only that week, since at that point I'll probably finish it.) I bought Luigi's Mansion 2 two days ago but I already logged 8 hours on it.
I always play games in short sessions, mostly 30 minutes or even less. (Sometimes 1 hour if I feel like it.) Nintendo games are the best at keeping me satisfied for playing short sessions, so I end up playing them the most, but it's not really exclusive to them. I don't get excited for many new games anymore, but their games have a lasting appeal, so that's why I always play them, and that's why I always play around 3 to 5 hours a week.