BK, I cannot believe you have never seen ZULU before! One of the great adventure movies of all time and all true. It may seem slow in the beginning, but they are carefully laying in and setting up all the background and exposition, so that once the action starts they're going Hell-Bent-Fer-Leather. Great performances...particularly outstanding is Nigel Green as Colour-Sergeant Bourne.
If you like it...you might want to check out ZULU DAWN directed by Douglas Hickox (he who directed my HOUND OF THE BASKERVILLES)...which tells the story of the massacre at Isandhlwana, which happened hours before the battle at Roarke's Drift. Fascinating history, compellingly, dramatically told.