One of the key aspects of most video game are the "animations". Typically, this is with respect to various people, animals, monsters, or what-have-you on the video screen. The best animations are life-like, fluid, respect the surroundings, and even use the environment when possible.
A game like Dead or Alive: Extreme Beach Volleyball has excellent characters models (probably the most life-like models out there today), but it does not have a rich set of animations. On the volleyball court, the women don't have a bunch of moves, though what they do have are very fluid and realistic. In some of the more voyeuristic modes, they move fluidly, but they still have a limited set of animations.
Compare that to a game like Ninja Gaiden. In that game, Ryu looks and moves with near perfection. His running, his flowing movement from one attack into a defense into a jump off a wall, how he wields nunchuks and swords... all of them done with a rich, flowing, and varied set of animations. He sometimes gets clipped by the terrain, but it rarely draws you away from the utter amazement of watching him move.
One the latest games that I just bought, BloodRayne 2, has got some truly amazing moves. The character model is also fantastic. In word, hot. In the initial levels, she has a long dress on which is slit on each side all the way up to here. Yah, perv: upskirts are there. What is amazing is watching her in combat with the dress and her hair flowing around her as she glides and spins and jumps from one stance or attack or defense to another. Very, very nice. I haven't played through enough to comment on game play (seems fine so far), but the graphics are quite amazing.
Other games with excellent animations: Otogi and Otogi 2, the Splinter Cell series, and even Psi Ops: the Mindgate Conspiracy. These are all amazing games and are excellent demonstrations of some of the best animations out there.