Marvel movies aren’t always fully coherent, but they sure do entertain. “Doctor Strange” is no different. Benedict Cumberbatch stars as a conceited surgeon who embarks on a painful journey of self-discovery after a catastrophic accident. Along the way, he learns to harness ancient powers — just in time for the fate of the world to fall into his trembling hands. Mind-bending effects add to the visual splendor. Tuesday’s Blu-ray adds a wealth of extras, including director’s commentary.