Most of my riding is out and back, technically it might be a loop since I go one way around lake natoma and come back on the other side of the lake, but it's what I do. I don't get bored since I am in the moment and just riding. I found even riding at night I can do loops and since it's dark I don't mind the same scenery. Each time I could take a different line, pass a different person, or see if I can power through the flat up the hill. Even playing music via headphones could give me a new experience.
I also enjoy seeing myself go faster up climbs, or carrying more speed through a section.