The only thing that really bothered me about fallout 3/nv is the enemy detection system, basically where they can stumble over the bodies of their comrades, and ignore the fact there are 6 dead fellows that you are silently killing right next to them. There are plenty of current, and even old games that have some sort of better threat ability that fallout 3 has.
Sadly in 3/nv there isn't any visual way for enemies to look for threats if they see dead bodies, or someone next to them is killed, etc. Other games like Deux Ex, metal gear solid, etc have visual detection where if a guard sees the body of another guard lying dead on the ground, they go into alert mode because hey, someone killed the guard and his dead body is lying right here!
Would hope there is something even remotely like that in the new FO4 so that i can't just sit far away silently killing a group of foes with headshots while they are just standing next to each other, or have enemies walk over the corpses of 6 of their fellows that i've killed and stroll along like nothing has happened. Would make stealth much more fun than the overpowering ability it is in fo3/nv.