Solid replies in this thread.
Let me try breaking down Duncan's game in his prime:
He was a solid 7 foot, 260 lbs with a round, not quite musculed frame and broad butt that allowed him to set up station on the pivot better than almost any other big in the last 30 years.
That enabled him to draw more fouls. As the Big Fundamental, Duncan had superior footwork and a larger repertoire of moves in the low post than even Hakeem Olajuwon. Duncan had a solid bankshot, though it waxed and waned. Post up moves topped by a brutally efficient right handed jumphook. Excellent spin moves, stronger left hand than most great post up bigs, and had a longer shooting range than almost anyone. Amazing handle, especially during face-up attempts.
Where guys like Karl Malone would go to a shaky turnaround jumper in the clutch, Duncan went to work on the low-post.