nice, bridge, I think the roof and the pillars holding up the roof might be a bit bulky and obstruct the view. Especially if you make a minecart track around it like koolio said, you wont be able to see the view properly (I know because I have built many rollercoasters on rollercoaster servers (chaos craft)). another thing is the corner wich is a bit derpy but that can easily be fixed or you could add a small tower. The last thing is that you could add sugar cane, that would help where the walls are a bit plain.
Cool how you have two floors though and I like how the cobble and brick come together, very nice.