I'm glad you enjoyed your first week of bike commuting!
One reason I like cycling vs. other forms of exercise is that I feel like you can go somewhere. During last weekend's charity road ride we went through 3-4 different towns. I felt like I went somewhere and saw things.* Want to go check out a waterfall--see if it's near a mountain bike trail. Want to see that pretty vista? Take your road bike and ride there. I enjoy seeing different sights. Want to go to the pub? Take your bike!
*I realize that you don't have to run in circles and can do a route running/walking, but you can go further on a bike.