The battle between Obi-Wan and Darth Vader in A New Hope was plodding and simplistic, a reflection of the era and the limited mobility of the Darth Vader suit.
The Darth Vader we see here is aggressive and vicious, playing for blood against his former master.
This is far more in line with what we have come to expect from lightsaber battles in the new films.
But this reimagining is far more in line with what we expect from two masters.