It just doesn't seem realistic. Sure, textures are extremely detailed, but I could've gone with fewer leaves in the trees if it meant a faster framerate. Clipping is also a problem. I actually managed to get Cynric in a tree. Getting him out was a challenge in itself.
Control is an uncomfortable, daunting task.
Circle strafing becomes an exercise with the shoulder buttons and pulling of combos results in sore knuckles. Granted, this is probably Sega's fault due to the DC controller design, not Treyarch's implementation of control. However, Draconus isn't full of faults. Take for instance the sound. You can tell that the Draconus team had fun doing the voices, and I'd love to hear the outtakes sometime.