For those of you interested in the differences between the early Marathon 2 Preview and the full game, I've converted the Shapes file from its "half Marathon, half Marathon 2" format into something readable by Anvil, ShapeFusion, and Aleph One. Get it here, until Hamish finds a home for it in the Story archives.
Bungie included some goodies that aren't visible in the actual demo. The Pfhor set, interestingly, is a nearly-complete remake of the M1 textures. The unfinished weapons in hand are also fun: the fusion pistol is an untextured 3D render, and the rocket launcher is wildly different.
This Shapes file won't work with the full game, as many monsters and scenery items are missing. It mostly works in Aleph One with the original Preview map, with the notable exception of terminals.