Recently I have been looking through Blendswap a lot and I found a model that really caught my eye, created by Bryan Fury on his blend called "Super mario bros". I thought for a while of a retro game I make 3D while still having a 2D look from a front orthographic camera. So I thought of space invaders! I hope you guys like it.
Uhm, I don't plan to make this interactive with BGE, but if you want to do that be my guest and I would love to see the end result. If I was to make it interactive I would use the Unity3d Engine..
My Space Invaders blend: http://www.blendswap.com/blends/view/73464 (57MB) Although I think Blender is amazing I don't find BGE very user friendly. Recently I've been experimenting with Godot Game Engine. If you're into Unity you should check it out. Godot is also very powerful but it's open source.
Retro games are great. Are you planning to make this interactive? If so, I also made a Space Invaders game a while ago. It contains some scripts you may find useful (the file is rather large (+/- 70 MB).