Ergonomically, SteelSeries' new Sensei mouse is just like its previous ambidextrous kit, so the upgrades are all under the hood: namely, a 32-bit ARM processor that doubles its max counts per inch from 5700 to 11,400.
(The industry standard term for sensitivity is dots per inch, but SteelSeries prefers counts per inch — regardless, the higher the number, the more sensitive the mouse. So at crazy high levels like 10,000 DPI, if you breathe on the mouse it'll shoot your cursor across six monitors.) Anyway, other specs: It's using a laser sensor and it can track movements at 150 inches per second, enough for giants to use it, and the grip's got a metal coating. Oh, and the other new feature — though I'm not sure it's an improvement — lights. Lots of lights. Everywhere.