I've never had so much fun in solo Marathon (or been so frustrated) as with the levels in this pack. The hard and twitchy gameplay on Total Carnage is the only thing so far that has inspired me to vid. If you want some great solo play with minimal background (or foreground), go for KTA.
Kill Them All is a short but intense mini-scenario for Marathon Infinity. It is a collaborative project, wherein the goal for each mapper was to make complete, high-quality maps that had no more than 100 polygons.
KTA features 15 levels by myself, screamingfool, Kinetic Turtle, irons, and Shadowbreaker. It's a difficult but action-packed game -- very fun.