The video is pretty dramatic.
One reason behind SpaceX's Falcon 9 launcher's being designed with 9 engines was to allow "engine-out capability." (Another was to allows mass production of small engines for the cost advantages.) This one is not just a shutdown, though - you can see substantial pieces of an engine bell (nozzle) flying off. NASA will no doubt want some more analysis and assurance despite the success. The other medium-lift rocket builders, Boeing and LockMart, have proven they can build superbly reliable rockets, although at very high prices. SpaceX is trying to prove it can build equally reliable rockets at much lower prices.