Depends. If I've got a brand new "hardcore" game, I tend to make time to play it over a few days start to end. If I've got a brand new "casual" game, I might put in an extra hour here and there just to unlock everything and have a go at all the content.
In a typical week though (where I don't have a new game), I'd be lucky to get in even 30 minutes a day. Gaming for me, especially in large amounts, is something I tend to plan. If I have a free Saturday coming up, I'll dedicate the afternoon to some gaming (this is usually where I start on my back catalog of "hardcore" titles).
To answer your question directly, I'd say around 4-5 hours a week average.