The new Marathon Phoenix is the best Marathon Scenario I have ever played.
One can only gripe that some level secrets can only be found via the PDF walk-through, or TABTABTABTABTABing every wall.
That is to say some secrets are not indicated by anything out of place.
S'PHTSTORM is the only bad level for its terrible game play. All enemies teleport in, the level would otherwise be uninhabited, so anytime you enter a new room, you get ambushed and DIE instantly.
The level can only be beaten via NEW ROOM+DIE+MEMORIZE+NEW ROOM+DIE+MEMORIZE+NEW ROOM+DIE+MEMORIZE=BAD GAME PLAY.
A 35-level single player major conversion.
This scenario is difficult and action-packed; it features a full arsenal of new, powerful weapons, and more threatening enemies than you could ever want.
1.4 has new Lua features like a performance overlay, weapon buffs, a lot of little bug fixes; it also applies ammo capacity limits on Total Carnage. Requires Aleph One 1.5 or newer, probably!