It seems that you're using an outdated browser. Some things may not work as they should (or don't work at all).
We suggest you upgrade newer and better browser like: Chrome, Firefox, Internet Explorer or Opera

I used to play the demo of ROTT over and over when I first got it. It had that slightly different feel to other FPS games of the time.
Overall level design is rather dull and boring, however, the game throws out some interesting stuff to change it from a simple shooter.
Various traps of spinning blades, and fire balls & Weapons, that create an enormous amount of gibs and damage. Enemies that play dead, and plead for their life.
Other new things were DOG mode. In single player at least, getting the dog power up, would shrink you down into a little dog. You could still attack, but there were extra hidden areas only normally accessable while changed.
The GOD power up would have you making long considering "Hmmmnnn" noises, while launching an attack that would seek out and vaporise all it touched.
Shrooms, would make the game slightly psychedelic and uncontrollable.
Jump Pads: There's no real way to describe these to those who have been jumping in games since year dot, but when ROTT was released, running high speed around a level onto these things and bouncing over the place was unusually fun. In multiplayer, it changed game tactics, as targets became more or less difficult to hit , depending on if you were in the air or not.
Also, there is a slight old style platformer feel, where you have to collect glyph-credit/coin-things. Grab 100, get an extra life.
While it is a load of fun, a lot of it is probably the nostalgia aspect for me. It might not hold up for others, unless you are really into the older FPS genre.