Players move the way they are supposed to. They dive when they should dive and it looks like they are diving. They juke, they cut, they pinch. It just looks good. Endzone celebrations and players gasping for air look believable.
Offensive linemen block the way offensive linemen are supposed to.
Running backs stutter-step when they have to. Very nice indeed. Of course, all this juking and diving and player-specific motion comes with a price. Madden 99 has a very, very steep tag in terms of PC power. The recommended requirements are closer to the truth, and it wants a PII 300 with 64mb of memory.