Already, that's a massive improvement on what was already good. The riffs now have character and individuality. A constant drum line is fine for something "atmospheric", like Burzum's Black Metal, but it doesn't work nearly as well in any other kind of Metal (which is why I'm currently finding Bolt Thrower's Warmaster to be a bit hard to get into - the drums just seem stagnant for much of it). Morbid Angel is the best example I can think of, when it comes to percussive dynamism.
If you were to lengthen that song, create a strong and epic narrative with the riffs, and perhaps add leads/vocals, it would be fantastic.