GPL with FSAA (top) and without (just above).
Look at the non-aliased version and note the jagged lines on the suspension, and the broken grid lines on the track surface. Also note the driver's "warped" visor, the "step" in the top of the left rear tire, and the jagged white line to the left.
In the next frame, as the car moves forward and the camera pans, all those jags will be constructed in a slightly different place on each line. As a result, the driver's visor will appear to warp the other way, and many of the other jagged lines will appear to squirm. The same artifacts in other views produce a very unrealistic "sparkle" effect.
Now look at the top shot and see how much smoother all the lines are. There's no warp in the driver's visor, and the lines on the track look straight and smooth.
Although there is an obvious difference between these two screen shots, the difference is much more dramatic in motion. The absence of jaggies in the aliased version produces frames that flow much more gracefully from one to the next. The sparkle effect is gone, as are the squriming lines.
With FSAA, the overall impression of GPL in motion is much smoother and more "movie-like". Driving from the in-cockpit view, the FSAA version is really gorgeous, a delight to the eyes.