Blessed Are the Sick is an excellent example of what made the early nineties brutal. While modern listeners have been spoiled by multitrack production and layers of sound, it is probably albums like Altars that are the most frightening and evil among extreme metal. The overt rawness brings an element of darkness pretty much unprecedented, especially at the time of its release in 1991.
Altars is my idea of everything necessary in Death metal. David Vincent's vocals are of course brutal, but again very raw, and not as deep as many death metal growls. The drums are prominent, and the bass kicks are probably the most prominent sound on the album. Trey Azagthoth's guitar has plenty of sophisticated lines, and have some pretty dissonant, yet screaming solos (check out the intro to "Abominations"). All the elements collaborate to create the next foundation of death metal, dark and heavy, yet dissonant and intelligent within that realm.
Also prominent within the album are the few atmospheric instrumentals sprinkled in the album. "Intro" brings in some truly terrifying pick scrapes and distortions, bringing in the album's grotesque tone properly. "Desolate Ways" is a somber guitar track towards the end, that properly highlights Azagthoth's sense of melody and composition. While a few build atmosphere wonderfully, some like "Doomsday March" or "In Rememberance" are a bit dated sounding or poorly put together.
Overall, though, most of the actual songs are great highlights. "The Ancient Ones" may be the best song on the album, featuring chromatic thrash type riffs in a very memorable structure. It also has plenty of searingly evil guitar lines throughout it, especially in the lengthier instrumental section. "Rebel Lands" is also very tasty, featuring some of the earliest examples of the 6/8 death metal blast, along with lyrics of war and desolation. "Fall from Grace" also pounds in to introduce the album furiously, before going into full-blown aggression. "Thy Kingdom Come" is probably the most aggressive song on the album with unrelenting blasts along with one of the most quirky and dissonant death metal solos you will ever hear.
The only flaw may be that to modern ears, this album may sound a bit dated. Which is true, at the time the recordings weren't able to put together the deep mixes available today. However, Blessed Are the Sick is still a haunting listen, and anyone who knows death metal should be able to look beyond that. That being said, It's already a classic landmark in death metal, so most fans should be aware of it already and be aware of it's evil presence.