This is very good!!!! I will never be able to use bryce/terragen or any other 3d stuff. I'm stuck on photoshop, lol.
In my opinion, the sun seems too bright to be producing those kind of rays. Maybe if you toned it down a bit and added some yellow-ish tones around it it'd look less off. But, it is 'uncontrolled light' so maybe it's supposed to be like that.