There has been videos and multiple other threads saying how op the DMR is (The boltshot is too but i don't get killed by it that often, it shouldn't have a higher kill range than the scattershot or shotgun though). The DMR not only has a vastly superior range than the BR or carbine, but it also has greater bullet magnetism, a higher RoF than the BR and superior range.
To those saying it's harder to use than the BR... no just no. I tried using the BR 1st and thought it was an good balanced weapon, not a great range and not much bullet spread. I then proceeded to try the DMR. I knew after about 2 mins of using it how imbalanced the weapon was, at long range it is used almost exclusively (few pros who advocate game balance use the Light Rifle instead). At medium range it easily outdoes a BR or Carbine, even at close range the fact it can outdo an assault rifle is laughable.
I wouldn't have a problem with the DMR being as OP as it is if it actually had skill in using it (and before anyone asks when using the DMR i won about 80% of all my duels but just like any person who has a sense of fair play i got bored of how easy and op it was so i switched to using the Carbine for medium and cqc maps and the light rifle for big maps).
The amount of votes and the amount of threads clearly show the DMR and Boltshot is clearly OP.
As for Gears of War 3 yes there was weapon balancing problems but the balance was a lot more balanced than Halo 4 is. The S.O.S and retro lancer received a lot of complaints but there were drawbacks in using it unlike the DMR.