While the series is a long-running success, most don't remember the original game. Why? Because it was far different than the game it is today.
The game was originally a fighting game similar to that of Tekken or Soul Edge.
In Japan the game is known as 三國無双(Sangokumuso) being a spin-off of another video game series.
So when the series came to PS2 they changed styles into a open-world action game. In Japan they called Dynasty Warriors 2 真・三國無双 (Shin Sangokumuso) which means New Dynasty Warriors. So Dynasty Warriors 3 was instead called New Dynasty Warriors 2 and so on.
Despite the one hiccup the series has remained pretty straightforward.