And yes, that's an understatement. Sassoon wrote a whole lot of war poems, and you won't find much glory and sacrifice. Nope, just death and destruction in his lines.
You might think that would get pretty boring after a while, but Sassoon's poetry argues that war is death in a lot of different ways. War kills people literally, but even those who are lucky enough to survive, and even those who never actually see a battlefield, suffer some kind of death. War makes it impossible for surviving soldiers to lead normal lives because it's such a cold-blooded dream-killer. Take "Does it Matter?" as an example; the soldier in the poem is still alive, but he's had his sight, his mobility, and maybe even his friends taken away.
A quick gander at the titles of many Sassoon poems shows just how often he talks about death and war; titles like "The Rank Stench of Those Bodies Haunts Me Still," "I Stood With the Dead," and "Suicide in the Trenches" are great examples of poems in which Sassoon talks about dying, while "Does it Matter?" finds him exploring a more metaphorical, less literal, kind of death. The end result is the same: war is the pits, and there's no way around.