Not bad... in fact it is very good for you first terrain, but it could use improving. I don't like the fact that rock suddenly end with underground dome doodad. You should have added stalagmites (or stalactites, I don't know which one are on the ceiling), to give it that underground feel. Also try playing with fog, it makes even the lamest terrain look good if used properly.
But I have to agree with Huuruka that not many things are visible because of bunch of rocks (my guess is: randomly placed all over the screen). You should have placed them with plan, maybe place less rocks, and I think it would look better if those in the back have increased height (Ctrl+Page Up). That's all.