I just started using Terragen this weekend, and so far I find it highly enjoyable. The possibilities might seem overwhelming as you start, and also a bit confusing as it takes a while to build up that intuitive feeling as to what works, what doesn't, and sometimes simply to figure out how something works in the first place. I love learning new things that way.
It seems that there is quite a vibrant and inclusive community of Terragen artists here, though, and I am looking forward to figuring out new things and taking part in these forums.
Here is my first picture - still some work needs to be done on it to add more levels of detail, and I am thinking of replacing the tree with a cairn, but it is quite satisfying being able to make something like this after just a few hours of dabbling.