Marathon Phoenix is a great scenario.
More Action packed than any scenario I've ever seen.
Textures are great. Well placed. Weapons have great variety, and each holds a special niche in certain encounters.
The levels are amazing too, enemies, architecture, and flow, all top notch...
...Except for "Escape Two Thousand." It's a level filled with nothing but dirty tricks and a badly placed switch that opens a door that you'll likely miss. After you memorize it, it'll still kill you.
F*** Escape Two Thousand.
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!