The SteelSeries Sensei mouse is a good albeit expensive mouse. It is definitely one of the best performing solutions out there, and is right up there with the Mionix 5000. Sensor wise the Avago 9500 based mice are still in the lead, despite having issues on some mats. The Sensei definitely works best on hard mats.
Overall the Sensei is a very well rounded mouse. The shape of the mouse allows for perfect control with a palm type grip, and it feels good to hold and use. With seven well performing buttons it will be good even for most MMO players. For FPS gaming the sensor does a really good job, tweaked back to low sensitivity it definitely matches the IntelliMouse Explorer 1.1 at 1000 Hz polling rate. And at medium to high sensitivity the Sensei is simply way better. There still seem to be some slight performance inconsistencies across the DPI range, but it is generally better than with the majority of laser mice out there.