The features are good , but I think you should improve the color of the background .Its quite dull. Rest is good
You can change your background. The text "Type in your long URL to get short URL" isn't so visible Adding some css to API page
The logo is good, try to change the background with clear design. Use css instead to formatting the font.
Please make "Type in your long URL to get short URL" either bold or in different color and also the color of the button "shorten" needs to be changed since it appears as if its already pushed and cant be clicked . I hope you understood what I am trying to say .
You have nice design, but I don't like SHORTEN button. May be you can change the color for the button and the "SHORTEN" text.