I checked some of my favorites and I think Tearmoon Empire did a great job:

The sky was soaked in the crimson light of the setting sun that glared angrily from the horizon onto the Grand Square of the Imperial City. At the center of this famed square loomed a guillotine, its crude and rusty blade dripping red.

For once it follows the same structure as one of the opening lines I spoke of in my earlier post that immediately hooked me:

“The sky above the port was the color of television, tuned to a dead channel.” (from Neuromancer, William Gibson)

Just as the sky is usually not looking like static, the sun shining down on something is usually associated with something positive, but here the sun is angry. Makes you immediately think that something is wrong.

And if the "angrily" in the first line wasn't enough to instill a sense of foreboding in the reader, the next line about the guillotine with the red blade is the point where I sit up a bit straighter and want to know what's happening. Great opening lines. 10/10