By the power of truth, I, while living, have conquered the universe.
DMR.
The BR slaughtered weapon variety (but I accept that there were a lot of redundant weapons in H3), it became the weapon everyone used and made matchmaking very repetitive. The DMR is ultimately a better weapon and at least we'll never be hearing complaints about the "spread" again.
The Needle Rifle is a very welcome addition too, the supercombine was satisfying but it felt great whenever you land a headshot with it.