It's a tie between Jinjer and Glassjaw.
Jinjer is a band which is a rising star in the metal world currently, I think the studio live video of "Pisces" has at the moment around 14 million views in YouTube at the moment. It was my gateway for the band also. I'd wager most people are drawn into by Tatiana's amazing vocals, but the whole band is insanely talented. They released new EP Micro last week and while it didn't really hit me like King of Everything did, I think the complexity of the new material makes it more of a slow burner.
Glassjaw is a post-hardcore band that I think had the tools to break into the mainstream in the early 2000s, but the record label screwing them over and vocalist Daryl Palumbo's health problems got into the way (also the lyrical content of their debut Everything You Ever Wanted to Know About Silence didn't help, it's been criticized for misogyny but you can take my word it's great listening when you're having relationship troubles
) They combine aggression and catchiness like few can do and their musicianship is top-notch. After 2002's Worship and Tribute, it took them 15 years to release another LP, but 2017's Material Control has all the makings of a modern-day classic.
I also want to mention another post-hardcore band Dance Gavin Dance, who released my two favourite songs of the last year (Care and Midnight Crusade). They are another very technically proficient band, even proggy at times and Will Swan is an absolutely amazing guitarist.
Oh, and Pantera! Why did no one tell me how awesome they are before? Dime and Vinnie are definitely among the best guitarists and drummers ever respectively. I started listening to them about a month before Vinnie Paul passed away
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Some other great bands I got into in 2018:
At the Drive-In (no I don't like post-hardcore or anything...)
Savatage
Christian Death
Faith No More
Ladytron
Autolux
Morbid Angel
Deicide
The Smiths