Many other big servers of that era were terrified of the Agassi return, and knew that if they didn't get their 1st serves in, they could be in real trouble on their 2nd serves.
However Sampras relished facing the Agassi return and Agassi in general. More often than not it brought out the best him, and he was always up for the challenge. He was perfectly happy to slug it out with Agassi from the baseline as well, because he knew that if he won those type of points, it would demoralise Agassi.
Their 4 US Open matches to me are the most of important of their rivalry. It was biggest neutral stage where they could battle it out. Each time Agassi was the clear favourite; in 1990 he was more established player while Sampras was still the 'kid', in 1995 he had won 26 matches in a row and had dethroned Sampras as the best player in the world, and in 2001 and 2002 he was one of the top 2-3 players in the world while Sampras was declining and suffering a long title drought. However each time Sampras won. As I said on another thread, those 2001 and 2002 matches in particular prove beyond any doubt that Sampras was simply the better player.