The thing I've found with running outside vs. the treadmill is that I'm a lot more natural outdoors. My treadmill runs are very structured - usually a set block of running time at a specific speed, followed by a minute of fast walking to bring my heart rate down. I repeat until I'm done my workout.
When I run outdoors, I listen to my body. That might mean I run for 15 minutes straight, or it might mean I run for a couple minutes and then stop and walk for a few seconds. Sometimes I run fast, sometimes it's more of a slow jog. It all depends on how I feel based on heat, terrain, muscles, geese in my way, etc. When I enter my route after, I'm actually pretty close to my normal treadmill pace, but it's definitely more of a mix of speeds and styles. My goal is to pace myself, but I like that it's a little more intuitive when I don't have a display screen telling me what to do.
I enjoy both. I look at the outdoor runs as being my fun 'me' time, while the treadmill sessions are structured training, so they both fill an important spot in my workout schedule. Structure helps me build my body up to what I'm trying to make it do, and the free runs teach me a lot about where my current level of fitness is at.
I'd say that if you want to see if you enjoy it, put on a pair of shoes and run outside with no set goals in mind other than enjoying the fresh air. I find that when I do that, I end up with exactly the length and intensity of workout I want at the end of the week - sometimes it's a challenging one, like this weekend's, and sometimes it's more relaxing.