It's a very cohesive album, not remotely the riff-salad you find in a lot of later tech/prog death metal. There are a few weak points (Textures is pretty wanky/slapped-together), but then there's stuff like the last couple minutes of How Could I? which is one of the best ways to close an album I've ever heard.
Just for the record, there is plenty of music, even metal, that I love that is admittedly sparse in terms of individual riffs themselves. I prefer A Pleasant Shade of Grey over Awaken the Guardian, for example, and the former really only has a handful of riffs over its 50+ minute duration. The Butt was the first to mention black metal in this discussion, but I'm not biased against black metal with great riffs. Most Mayhem succeeds in part due to their excellent riffcraft, but they have other qualities that elevate them further. Show me black metal that doesn't rely primarily on 1) that overused 6/4 march and 2) tremolo picking that follows the beat lock-step, and I'll give it a shot.