SCUBA-2 is a revolutionary 10,000 pixel wide-field submillimetre camera, recently commissioned and now operational at the James Clerk Maxwell Telescope (JCMT). Twin focal planes each consist of four 32 by 40 sub-arrays of superconducting Transition Edge Sensor (TES) bolometers, the largest combined low temperature bolometer arrays in operation, to provide simultaneous imaging at wavelengths of 450 and 850 microns. SCUBA-2 was designed to map large areas of sky more than 100 times faster than the original ground breaking SCUBA instrument and has achieved this goal. In this paper we describe the performance of the instrument and present results of characterising the eight science grade TES bolometer arrays. We discuss the steps taken to optimise the setup of the TES arrays to maximise mapping speed and show how critical changes to the sub-array module thermal design, the introduction of independent focal plane and 1K temperature control and enhancements to the cryogenics have combined to significantly improve the overall performance of the instrument.