When I run I feel like I have a purpose, like I'm doing something worthwhile to fill gaps in my life. The process of pushing myself and doing something constructive makes me feel good.
I enjoy learning about the whole concept of running, having said that I do feel I have an addictive nature, when I enjoy doing something I tend to go 110% at it and need to know everything. So far thats been a good thing which has also benefitted my training partner as she has enjoyed being left to run while I plot the workouts, read the training plans, pass on the tips etc etc. Everyone wins.