After reading though this, the adventure makes perfect sense. I think it would be pretty straightforward and fun to pick up and play.
The cover art looks good to me for the most part. Having Vast and Trunkless first and larger than Mercy in the Ram's Hall makes it seem like "Vast and Trunkless" is the title and "Mercy in Ram's Hall" is a subtitle, which confused me a little at first. Also, I think you should do away with the curve in the ax handle above the shoulder.
I think this sentence could use some cleaning up, "The shepherd became the lords Carnifex, and, Each winter, the serfs were to elect a champion to challenge the Carnifex, or risk joining the lords' obedient herd." "each" should be lowercase, and "lord's" instead of "lords'", unless there are multiple lords. Also, I think "risk joining the lord's obedient herd." could be clearer, do you mean all the nomads would become his servants and no longer allowed to wander?
OK, based on that they're growing horns, I'm guessing if the pact isn't fulfilled they all turn into sheep.
"The cell is overwhelmed with a weathered, huge blue-skinned man with bull horns in undergarments" Initially, I read this as him having horns in his undergarments, haha.
The layout on pages 2-4 is perfectly serviceable. I wouldn't think anything of it if this was an adventure I bought but for the purposes of the competition it's not a dynamic visual design. Maybe consider a more weathered page background as a quick change to add more flavor. One thing, I would like to see the map and the writing on the map to be a bit bigger to improve legibility.
Hope this helps, it seems like a super fun adventure! I could see myself playing it. Let me know if you have any questions for me.