Your doors are good, but the colors are soooo boring.
http://pixelcocktail.com/HKCP/Working/B ... help04.png[/imgzoom]
(the shadows are one dark color, but they've been put on a transparent alpha layer)
If you add some color, it doesn't take away from realism, it makes your tilesets look interesting. It makes them exciting!
You don't have to use this, but I wanted to show you how the colors play together at different saturations.
Also the rivets in the door's railing could use a little more smoothing on the outlines, which would be helped by small shadows under them. Also the HKCP Standard lighting angle comes from the top-left, so there would be a slight alteration in the rail's shading and the shadows cast by the stone archway onto the rails.