Neat project. One critique: I don't like having only five lines of the snippet visible at any given time, it makes it harder to easily understand what's going on in some of your longer snippets.
I suspect that the five line limitation was done so that the "Give me another one!" button was always in relatively the same place and easily clickable (I appreciate that), but perhaps there could be a small, duplicate text link up above the snippet for this purpose too, thereby also letting you make the snippets longer.
I like the idea. Yes, there's the need for both. I'm thinking about just making the text size variable according to the number of lines in the snippet - I think that makes more sense.
That's a thought, but even moderately sized snippets might get hard to read. I think this concern is especially valid because the rest of the text on the site is large and easily readable from a distance, so making the most important text–the snippet–smaller would be out of place.
Just change the layout. The 'play' button and execution results are equally logically placed under the code. That should give you enough space for snippets of any size.
I suspect that the five line limitation was done so that the "Give me another one!" button was always in relatively the same place and easily clickable (I appreciate that), but perhaps there could be a small, duplicate text link up above the snippet for this purpose too, thereby also letting you make the snippets longer.