The second riff in this tune is what I'd call a "thrash" riff. In my mind, the main thing that describes a thrash riff is the back and forth interplay between the kick and snare (again, it's subjective, you might use a different descriptive word).
My main concern while playing this riff was to make sure I had accented notes on the 5th string. The way I acomplished this was to not use straight alternate picking. I noticed right away that I wasn't getting ideal phrasing when I used alternate picking but with one added down stroke I was able to achieve the phrasing I was looking for.
Those are just a few things to consider while learning this riff.