The first true 3D FPS enviroment that allowed players to walk on and under the same platform.
This title was built on Wolfenstein 3D's engine and was released about the same time as Doom. Doom's heightlevel and non-orthogonal engine, however, stole the limelight from ROTT, sort of.
ROTT was renowned for it's extreme violence and it's (for the time) very realistic sprites, much more so than Doom's. The violence, on full, provided showers of blood that rained down after enemies were blown up with rockets. A special Gibs code allowed fro even more blood spray. Eyeballs were also amongst the gibs and occassionally you could spot a decaptitated hand giving you the finger.
This brings me to another great little feature of ROTT. Missile and Rocket Luanchers. There were several ones to choose from. Drunk missles, heat-seeking, rockets, firebomb rockets, flamewall rockets, and a split rocket that divided into 2 heatseekers. In the gun department you were given an MP40 and a handgun, both with unlimited ammunition. If another handgun was found, you could dual weild the handguns, John Woo style. There was alsoa baseball bat and a wand that shot magical orbs and made you invincible for a limited amount of time. There were other items that let you fly or jump really high as well.
The levels were designed square by square (since the engine was a modified Wolf3D engine), butthere were several twists. bits of the walls could move back and forth and heightmaps were added. There were also floating platforms that could be adjusted to create stairs, moving platforms, as well as walkways that players could travel ontop off and underneath! Which was a very big improvement at the time.
It was rumored that ROTT was actually suppossed to be a sequal to Wolfenstein 3D, but was, for whatever reason, axed and released by Apogee as is.
The story is pretty vague and nonessential (just like FPS's of today!) and involved something about a special forces team named H.U.N.T. going to som island, I think. I remember you could choose which character you wanted to be, which affected your aim, height, run speed, etc.
Another fun element was that the game would read your system date, and if it was a holiday, the load screen would have the chars wear hats relative to the holiday. There was also a rock 'n roll christmas carol that played on christmas.
A very fun game to play, and very hard too. Did I mention that there's poison gas, flame traps, spinning blades, spikes and all sorts of other traps? No? I'm pretty sure I mentioned the horrible and excrutiating pain.. yes, I'm sure I did.
Next time you're at a LAN party and wanna wow some n00bs with some old school obscure FPS freg-fest fun, whip out ROTT and show 'em where gibs truly came from!