I found more screenshots. Still can't build anything. One thing that is definitely bad about XNA, porting projects from one version to another always sucks way worse than it should.
Anyway, this was going to be a side-scrolling shooter with lots of different vehicles that you could roll around in. I think I spent most of the time on this one just doing really weird stuff, like the terrain, physics, and animation were all pretty non-standard and programmed from scratch. This was from a time when I enjoyed programming in its own right and didn't think very hard about how games work.

Like helicopters and jeeps.

Boats and soldiers. There was actually a lot more artwork done for this (by krinkels in fact). Animation for all the characters and units, buildings, props.

Some physics.

Each team had bases where you could buy vehicles, it did this cool thing when you entered a base where the game didn't quite pause but just went in extremely slow motion. Awesome.

Some kind of totally unnecessary particle effect editor. There was a skeletal character animation tool too with keyframes and stuff.

Terrain editor. This is the pinnacle of weirdness in my design. The terrain was defined as a sequence of polynomials, so there would be a poly for the first 100 horizontal pixels, then another for the next 100, etc. I had a shader that could then render the terrain smoothly at any magnification, just like how vector graphics still look smooth when you blow them up. Having the polynomial also allowed me to calculate the normal at any point for physics by taking the derivative, and I also reparameterized it with respect to arc length in order to figure out where a soldier walking either "left" or "right" should be on the curve each frame. (I was taking calculus when I was working on this.) I'm sort of proud of the mathematical cleverness but really it was a dumb idea, when you make games you should just do everything in the most simple, proven, off-the-shelf way possible unless there's a specific reason to do otherwise that is based on a well thought out game mechanism and will directly result in fun.