It has nothing to do with the interludes, one of which I find bad (In Remembrance), one which I can never decide if it sounds awesomely creepy or silly and cheesy (Doomsday Celebration) and one of which is great (Desolate Ways). Released in 1991 I can't really think of anything that sounds like Blessed are the Sick from that time period. The album is very cohesive and I've always found it to work incredibly well as an album experience - the track ordering and the pacing is pretty much perfect. It's quite a large change in direction from Altars, more mature and more varied in its tempos and lyrical content. What it lacks in the youthful energy it more than makes up for in its artfulness imo. They took a step back come Covenant where most of the songs on that album are about hammering brutality and Vincent's vocals became more about being as brutal as he could be, rather than intelligible and charismatic.
What's shit about them? The best album won. Human is too low and Symbolic is too high is my issue.