No its just one of the best marketed. I'm not putting Krav down but you will find just about all of its techniques in various other martial arts from around the world. What some Krav Maga classes do well is the pressure testing and scenario drilling of techniques to try and make them as applicable in a real confrontation as possible. This did not start with Krav Maga nor is it unique to it.
Most martial arts originally were developed in a more violent time than in most western countries today. All of them have techniques that are designed to kill or to break bodies. As the American self protection specialist Rory Miller states "The study of martial arts is the study of the manufacture of cripples and corpses" He is not claiming that you should always go that far in a fight but that the original intention of many arts was to take life from someone trying to take yours (read his books in fact or even better go train with the guy if you get the chance and you will have a better chance of defending yourself without ending up in prison).
viscous [vis´kus]
sticky or gummy; having a high degree of viscosity.
I would be hesitant to apply that term to any martial art(though I could think of a few that it might just sorta work for)
vicious on the other hand depends on the person using it not the style itself vi·cious (vshs)
adj.
1. Having the nature of vice; evil, immoral, or depraved.
2. Given to vice, immorality, or depravity.
3. Spiteful; malicious: vicious gossip.
4. Disposed to or characterized by violent or destructive behavior. See Synonyms at cruel.
5. Marked by an aggressive disposition; savage. Used chiefly of animals.
6. Severe or intense; fierce: a vicious storm.
7. Faulty, imperfect, or otherwise impaired by defects or a defect: a forced, vicious style of prose.
8. Impure; foul.