In Deep Down's reveal trailer, a band of armored adventures cautiously made their way through some shadowy ruins before facing a giant fire-breathing dragon. The battle that ensued was a glorious display of next-gen particle effects (you can thank Capcom's new Panta Rhei engine for all the pretties).
For a more accurate representation of Deep Down's gameplay, however, you need look no further than Capcom's presentation during Sony's pre-TGS conference. Here, you can see a lance-wielding warrior fight a few ogre-looking creatures. Notice the crosshairs in the video? You can actually aim your lance thrusts (and, presumably, the strikes of other weapons), perhaps allowing you to cripple enemies by attacking their appendages. Every time a strike lands, floating combat text details your damage output. Judging from brief glimpses of the UI, it appears you can equip different types of weapons and items, allowing for quick swaps on-the-fly. The whole thing has a sort of Dark Souls vibe, especially considering the reveal trailer ended with the tagline: "Conquer your fear or die a coward."