Its not the same game, pay attention to the characters, all of their movesets are refined. Taki plays even more like a ninja for example. Raphael's fencing style is even more refined.
I think it takes more than 15 minutes to appreciate what changed.
And how could you not notice the difference in the "SPIRIT" of the game which is more like Soul Edge than ANYTHING that came after. The stages alone are awesome, but the story is awesome and branches too I think. COME ON!