There are a few things that make something OP to me; 1. There is no concrete counter in general, or without an insane amount of dedication. Ghost's thermal and tracker sights spring to mind here, as the only effective counter is not only extremely short lived (smoke and Incog together), but also takes up 4 perk slots alone, not counting any weapons you want to use. 2. They overstretch their intended role, some SMGs in various games that reach too far or some snipers that are really consistent up close without much sacrifice in return. 3. Rewarding otherwise bad play, Titanfall has Nuclear Ejection and Smart Pistol, as a good example. Martyrdom from older CoD is also a good example, as are Death Streaks. Albeit these can be lumped in as annoying, and I don't find Nuke Eject extreme, but :P 4. A mechanic or weapon that overwrites other weapons in terms of effectiveness is kind of a case by case type deal, but some I would say are nerf-worthy, others would need the exlipsed weapon seeing a buff. Good examples are really any systems that are one hit melee mechanics, at least from front. Titanfall 2's basic melee spring to mind. I can also kind of argue certain supply drop weapons from CoD (Rangers, K-12, The MWR DLC bolt action sniper, AW STG, WWII VSTG, Blops 3 Peacekeeper I'd also lump in there, and I'd hear arguments for a few other Blops 3 weapons). I feel like Destiny 2 is the kind of game that is trying too hard, I definitely like balance, but D2 isn't trying the MW2 route, where everything is OP at something, albeit some weapons have more desirable combinations than others. I don't really have anything that I'd explicitly Nerf in D2 right now, albeit the 450 autos are only as good as they are because of map size, or so I theorize.