Credit to Bootaay of Neogaf for compiling the images:
http://www.neogaf.com/forum/showpost.php?p=15295800&postcount=145

Graphical Evolution of the 'Warriors' series of games

Dynasty Warriors



Dynasty Warriors 2



Dynasty Warriors 3



Dynasty Warriors 3 Xtreme Legends



Dynasty Warriors 4



Dynasty Warriors 4 Xtreme Legends



Samurai Warriors



Dynasty Warriors 4 Empires



Samurai Warriors Xtreme Legends



Dynasty Warriors 5



Dynasty Warriors 5 Xtreme Legends



Dynasty Warriors 5 Empires



Samurai Warriors 2



Samurai Warriors 2 Empires



Warriors Orochi



Dynasty Warriors 6



Samurai Warriors 2 Xtreme Legends



Warriors Orochi 2



Warriors Orochi Z




Dynasty Warriors 3 will always remain the most awesome in my heart. But yeah, the engine never changes does it?

Playing through the games, it's evident that the engine has gotten tweaked over time, and Dynasty Warriors 6 actually does use a brand-new engine, but yeah, it's remained relatively unchanged at its core for most of the series.

Isn't that Dynasty Warriors 2 shot from the fifth game?

Erm, Ling Tong wasn't playable until DW 5. 
 
But, yeah, Dynasty Warriors doesn't change much. Still love it though, haha