I personally think that doing anything outdoors is better than staying indoors, IMHO, but this is just moi, so don't everyone jump on me here

.... I also love running and am now hooked after 1 yr 4 months of running... Here is a good article I just found:
http://www.fitfaq.com/running-good-exercise-choice.html
Quote:
Why Running Is A Good Exercise Choice
Learn why so many people choose running as their primary form of exercise...
Perhaps I'm just a little biased. I do, after all, enjoy running…whether it's on a treadmill or in the Great Outdoors! But, aside from my personal endorsement of running, there are lots of other great reasons why running is a good exercise choice.
To obtain optimal health, you should ideally engage in exercises that will strengthen the heart (a strong heart helps reduce the risk of coronary heart disease) and lungs. You should participate in exercises that strengthen and tone muscles, as well as increase your energy level. Exercising regularly can help you maintain a healthy weight and simply help you feel and look better. In fact, a good exercise program has the ability to add a couple of years to your life! Additionally, people who exercise regularly, tend to be happier and laugh more, because exercise alleviates stress and anxiety. And, when a person attains better health through exercise, that person will generally have a healthier, more optimistic outlook on life.
Benefits of Running
But why pick running as your exercise of choice? First of all, running is a wonderful aerobic exercise. And, aerobic exercises are great for improving one's cardiovascular health. Running is also a good way to burn calories and to control your weight. Consequently, runners can develop those slender, sleek, toned bodies many of us desire. Also, if you're involved in other sport activities, running will help you benefit in those activities, as your aerobic fitness and stamina improve.
Another reason that running is such a perfect exercise of choice is that virtually any healthy person can do it! Practically no special skills are required. It is ultimately dependent upon no one else but you. It is your own willpower and determination that drives you to run and allows you to reap the benefits of running. Running can be carried out virtually anywhere, anytime. All that is really needed is the desire and the will, a good pair of running shoes, and some inexpensive, comfortable exercise clothes.
As running improves your fitness, you will likely discover that you have more pride in yourself. You will learn to appreciate your body more. You might even surprise yourself with your own capabilities and with how much you can achieve when you run. As a runner, your self-reliance, self-consciousness, and self-commitment may also increase greatly.
Treadmills are great machines on which to run, if you prefer an indoor workout (i.e. at your local gym or in your home or office). And, a good treadmill will provide a low-impact, aerobic session any time of day and any time of year, regardless of the weather.
On the other hand, not everyone has access to a treadmill or can afford to go out and buy one. Running outdoors costs nothing. You may run along the streets of your neighborhood. You might find a park, which has trails made specifically for running. Or, perhaps you're more of an adventurer and prefer to run cross-country. For the nature-lover, outdoor running can also be very calming and soothing…sort of a meditative experience…depending upon where you run. You have time to yourself…time to think…time to notice the world around you.
Before beginning any exercise program, it's a good idea to consult your health professional to make sure it would be safe for you to do so.
Cyndi Schoenhals
Hope this helps...