This is a slightly different blog post and Smith and Winston. I'm going to show how our game editor works (and thus how our engine works). We've spent a lot of time getting the editor setup to make it easy to create game play.
I posted most of this to TIG Forums but thought I'd reproduce it here for people that don't want to read a forum.
I evaluated Unity3D for a few months before deciding NOT to use it. It's a really, really great tool and it was a tough decision. Ultimately I felt like there was more resitance to steady progress using Unity3D over extending/upgrading my own code. Here is a rough guide to why I decided not to use it.
I'm currently writing an editor for our next game. We've used many tool in the past (Blender, Tiled & Mappy) to make games but we thought it was really time to invest in our own code base. This was heavily influenced by the great experience we had using Unity3D to prototype our next game.
If you want to cut to the chase you can download the code here.