That's pretty nice..Simple and effective. 

Ya know what I think would be cool, to build something like that, but have the fire cage/pit on some sort of a crank system so it could be raised and lowered as needed.  I'm not mechanically inclined enough to build it though.  

In your case, if you had the walls built with the bricks, you could have a crank on the outside of the brick that you just crank and raise and lower the fire wherever you want it.  

If you're out there just enjoying a fire, crank it all the way up so its sitting high on top of the oven/firepit for visual appeal and warmth in autumn.  When you want to do some serious cooking lower the fire back down into the hole that you dug.