Keeps you asking for more. After all these years, I still enjoy playing.
Each race has two new units, each making the game even more unpredictable. The Terrans can heal, the Zerg can be even more disastrous, and the Protoss can control opponents minds.
The gameplay is more or less the same, yet your opponents have different strategies than last time. They build up a little slower, but they attack much faster. Many a battle has been lost before a single attacking unit is built.
The storyline is, of course, much more dramatic. Yet the storyline compels you to play more...