Neat, the VIOS and different Icon of Sin were unique at the time, also tying it with Wolf RPG with Stan Blazkowicz protagonist. This game also mixed classic Doom2 features with Doom 3 elements and it works here as perfect blend. One of unique characters introduced by this game was Kira Morgan, not typical Doom girl attempt but full blown person. I just wish someone would make addon of sorts just with that character's sprites and HUD face for normal megawads to play, voice clips would be issue though, as I remember there were not a lot of them even if you played as Doomguy or the Scientist but someone made connection with Crash from Quake3. The game gets harder later especially first ambush, in hell and Spider-Mastermind battle, but that Soul Cube was almost a missed opportunity, never really was forced to use it more than once and just for Cyber-Demon seems a waste.