Halo 4 is the better multiplayer game IMO. Good spawns, great hit detection and better game modes. However I rather play blops 2 despite its obvious flaws because it has more maps. Screw haven. Halo needs a map pack or custom forge maps ASAP.
Obviously, but what is decent is subjective, what you might find decent, I might not and vice-versa.
The best way to get a "decent" scope is to go with what's realistic, in CoD it's modern day / slightly futureistic weapons and scopes, so it would be realistic to aim down the sight like you would in real life at this point in time.
In the future (like 300 - 400+ years) weapons and scopes will change hugely (presummably) so having a "scope" that can hold your entire line of sight is entirely possible, and it is set a long time in the future after all, you kinda have to go into it with an open mind.