14 failed attempts on Cataclysm and counting. The final phase is overtuned and near impossible to complete with pug level players. Here are some suggestions on how to make the final phase more doable:
Lower adds, or allow the scythe attacks to friendly fire enemies (like all other bosses can). Low damage comps literally cannot keep up with the stream of marauders.
Change the ring of fire to random radii, similar to the earlier phases. Kiting enemies over rings as they explode to clear adds rewards good positioning. Doing this in the final phase is less viable because you are always at danger of being scythed and knocked back.
Make Nurgloth stop to channel the ring of fire like he does in previous phases. This prevents unavoidable scythe into ring of fire deaths (and the other way round). Also ties back to 2., making kiting enemies into it easier. It would also be a damage opportunity, which the boss currently lacks.
Reduce the knockback on scythe attacks. This attack currently guarantees that the person kiting t he boss has almost zero opportunities for damage. Reducing the knockback on the ring of fire is less important, but would be welcome as well. It is not uncommon to get knocked back into a pillar, allowing enemies to pile up beneath you on the ground.
I am certain that by fixing even one of these issues, the fight will be shifted towards a similar difficulty of other Cataclysm finales. As it is, the fight is not only too difficult but also incredibly punishing to certain loadouts.