The main character is a fallen angel named Bob. Bob has been lured to Earth as part of the Devil's intricate plot to suck the planet into hell. Bob possesses the unique skill of being able to jump into the bodies of humans and take control of them. Messiah is part puzzle solving, part action game, and part platformer.
The game introduced scalable changing of polygon detail, called Tessellation. Before, characters in the games were stored as static polygons-figures. Marketing materials stated the RTDAT (Real-time Deformation and Tesselation) engine could render unlimited detail, audio tracks, animation frames and level sizes, which was obviously only true up to a point - several years of delays meant that upon the game's release in 2000, the graphics that would've been mindblowingly detailed in 1998, had almost been caught up by traditional methods.
After modelling the characters they were compressed and dynamically created for each frame, according to the capability of the pc it was running on. In other words, the player would always have a constant framerate, while the quality of the visuals would dynamically adopt for each frame - always attempting to use all available computer resources, without overburdening it.
The game-developer does not have to crop down the quality of certain elements for the sake of the framerate for each loaded level, but he could model every element of the game in an unseen high rate of polygons before it would be compressed.
During the gameplay the player would not experience a slowdown.
You had true volumetric lightning in the game and also texture video streaming which made for some novel effects inside the game. "Film"-footage in the background, a stripper dancing, advertisement.
When Messiah was published there was nothing in the market that could compete technology-wise and it looked like nothing people saw on their computers rendered in real time.
Still the game was unappreciated and underrated since many people seemed not to relate with the main character and the humor.
Another underrated element was the gameplay. You had dynamic gameplay in a single-player game. Every encounter could be different on replay. It was not linear, nor entirely predictable. Enemy Characters had different behaviors and on top of that you had the great game-element to let you as the main character "possess" NPCs and switch from one character to another, giving you interesting tactical possibilities.
The game had a nail-gun as a weapon allowing you to shoot at a NPC and if you did hit him, he would be pierced and flying through the air would be pinned on the wall, hanging down in agony. There was nothing equal on any platform at that time to see.
Messiah was the first game that required a AGP-graphics-card introducing Transform and Lightning (T&L) to gamers.