I'm really liking this and I hope you add the characters in there too when you're done too.
I'm really not a fan of the dithering. You might be better just using solid colours to use for your shading as opposed to dithering. I'd look at other iso art and see how certain shapes and highlights are commonly approached.
I did notice a 4 pixel line on the roof of the bridge and another one just above the second bridge support (red side) were these intentional?
I don't think you'll obscure too much though, you can always take an artistic license and just make the bridge longer if it doesn't. Infact from looking at screenshots your bridge probably is a bit short. There's 4 support posts in yours and 5 in the actual one so there you go, problem solved.