Any of the supernatural beings in the Uncharted games.
Honestly, those things at the end of Uncharted gave me much, much less fond memories of that game. And even worse, at the end of Uncharted 2 i was desperately hoping that they wouldnt screw it up wi- Freaking Yeti? And after a while - Freaking Blue Guardians.
In a action adventure shooter set on PLANET EARTH, I want to fight proper bad guys. Different kinds of bad guys, sure. But HUMAN bad guys. What i do not want is Gollum's freaking family reunion, the snow monster from The Empire Strikes Back, and freaking ancient smurfs on steroids with crossbows.
Now, fantasy games, RPGs, RTSs, that's a different story. The can have all the freaking Smeagol smurfettes wearing goat fur all they want.