Why do my objects look like this in solid view?

@sobe608 was right, but for another reason. The faces are 'occupying the same place' .. but not in Object space; in the View volume. And they're at 'the same Z' (depth) in that volume, because the near and far clips are too far apart, resulting in floating-point numbers not having sufficient precision to distinguish points in the range.

TL;DR...

Change the clipping range in the viewport to the minimum that reasonably encloses your scene.

Looks to me like shading issues. Run the 3d printing checks and fix everything that gets flagged, with the exception of overhanging faces, which you don't have to fix.

Also, you may have multiple objects occupying the same space, which can cause a shimmering effect.