The first LEGO walker was really cool, however it was more a single printed toy of the same size and scale of a LEGO mini-fig and not a LEGO toy in its own right. Looking around thingiverse a bit more my nephew and I found this walker design, which snapped together as a series of four custom LEGO pieces.
http://www.thingiverse.com/thing:462844
It is hard to make out details because I printed it in black ABS, but this walker really came out pretty sweet. I think I will modify this design before my nephew visits next, making the legs more easily detachable – but still – it was still really cool to be able to sit down with my nephew, pick out one toy to make from hundreds of possible options, and then just print it. I mean this is what the world is like when he is 8, he is growing up with that kind of magic being the reality of his world. How cool is that.