Dimmu Borgir; Mostly anything stormblхst and before, In Sorte Diaboli was disappointing however Abradahabra was interesting.

Nile; Mostly known for their extremely fast, complex, and unique instrumental. Dropped A guitar and bass tuning, enough said.

Ne Obliviscaris; their debut album was very impressive for being what it was, despite belonging to such an extreme genre of music it still sounded beautiful and rather exquisite.
I can't get enough of the violin.

Megadeth; without a doubt one of the most known metal bands, their albums have mostly been hit or miss throughout the years but I have high hopes for Super Collider.

Soulfly; Sepultura without Max isn't the same. The sheer fact that Max stuck with his roots and incorporates tribal and world music into his songs is great and gives the band a unique sound which differentiates it from others in the same genre.

Honorable mentions; Pantera, Opeth, Kreator, Exodus, Amon Amarth, and Dark Tranquility.

also it'd be great if you guys gave reasons.