Bierce's style qualifies as both descriptive and ambiguous. He provides a lot of information but also withholds important aspects of the story. Here are just some of the story's components that are described to us in great detail:
Because Bierce provides so much information about Farquhar's situation, it is even more shocking that we don't know Farquhar is dead until the very end of the story. Ambrose Bierce sure put the "amb" (and the "big") in ambiguity.
Still, our first time reading the story, we don't quite realize things are ambiguous. So let's focus on the "descriptive" aspect of Bierce's writing.
Bierce's description of Farquhar's hanging is particularly detailed. It seems as regimented and precise as the soldiers performing the execution and the military code they follow. Bierce tells us exactly how the hanging works, down to the little detail about how the soldiers hold their guns:
A sentinel at each end of the bridge stood with his rifle in the position known as 'support,' that is to say, vertical in front of the left shoulder, the hammer resting on the forearm thrown straight across the chest – a formal and unnatural position, enforcing an erect carriage of the body. (1.1)
Bierce's attention to detail also extends to what it feels like to be hanged (though we can't comment on whether or not his description is accurate). Take a look at this diagnosis of Farquhar's state after he falls into the water:
Keen, poignant agonies seemed to shoot from his neck downward through every fiber of his body and limbs. These pains appeared to flash along well-defined lines of ramification and to beat with an inconceivably rapid periodicity. They seemed like streams of pulsating fire heating him to an intolerable temperature. As to his head, he was conscious of nothing but a feeling of fullness – of congestion. (3.1)
Bierce was a newspaperman so he knew how to drop a lot of knowledge in a really concise way.
However, Bierce doesn't just give us the cold, hard facts. He waxes poetic when he describes Farquhar "encompassed in a luminous cloud, of which he was now merely the fiery heart, without material substance [swinging] through unthinkable arcs of oscillation, like a vast pendulum" (3.1). In a sea of majorly precise and often brutal detail, it's nice to get a break and read some slightly more poetic language once in a while.