While there is some functional overlap (they are both skinnable app launchers if you pin the .exe files in Tiles), The latter's functionality is more flexible in my thinking and automatically finds and applies the skin you're using.
Also, Tiles is more intuitive and visually oriented, allowing work without constantly going to find whichever dock the particular app sits in, as well as allowing multiple customizable windows to be opened, minimalized and worked on without needing the taskbar.
These are just initial impressions. I have docks and Nexus docks/subdocks and Tiles seems to have (for me) precluded the need to have to run back and forth from open apps to docks.... and has made it easier to 'find' the fifferent apps involved in my work.
Me likes!
