You can actually go into surprising depth with Scratch. For example, I wrote multiplayer game engines using cloud variables to store player position, chat, etc and let people play together live. People have written 3D platforming engines using the "pen" feature, which is like a Python turtle. Hanging out on the "Advanced Topics" forum lead me to hacking with JavaScript and Python, at first to interact with Scratch and then onto bigger things outside of Scratch.
I think that Scratch is really great, if you couldn't tell from my description. Not only is it easy for a kid to get started with a drag-and-drop interface, but you can do so much. It also has a supportive community and it's easy to make friends and collaborate on projects together.
If you want to see Scratch truly at its limits, take a look around Griffpatch's profile: https://scratch.mit.edu/users/griffpatch/