It’s hard to say who the best metal drummer is, but Schalk is one of the best, if not one of the most unique. Besides a lot of what Sean Reinert or Justin Foley did in Red Tide, Schalk was one of the only metal drummers than I know of who incorporated a lot of jazz elements.
While Candiria was a mix of a lot of things, metal being only a part, Schalk eschewed a lot of metal drumming conventions: there’s no blast beats and rarely any double bass. He made up for it with some odd time signatures, or at least tricking you into thinking there was one by messing with the up- and down-beats, the aforementioned freeform jazz, establishing a solid groove instead of accuracy and speed, and playing “over the bar.” Standard drum fills end on the last beat, but playing “over the bar” continues the fill into the next measure. It’s a great way for the drums to add texture and play along with the instruments or vocals might be doing. Schalk actually has a video on this idea.
For an amateur analog video, this isn’t too bad in capturing the drum sound, and you can see clearly what he’s doing. What’s one thing to note about his drumming, is he eschews a lot of economy of motion standards. He brings his sticks back a lot more than other drummers, and there’s a lot of shoulder movements instead of keeping as much as he could in the wrists. I wouldn’t say it’s bad, just unconventional. A lot of those motion rules were probably established so the drummer doesn’t wear himself out, but Schalk looks fit enough to handle the cardio.