On-the-fly sensitivity worked fine, although the OSD associated with it did not. Separate X/Y sensitivity is adjustable, you can create multiple configuration profiles, and the breathing Razer logo and blue racing strip lights on the scroll wheel can be turned off if the bling annoys you.
There are macros too, but just like the Abyssus they're next to worthless, only storing 16 events.
Firing up Serious Sam HD, the Imperator dispensed justice with ease, offering an incredibly accurate and smooth experience. Whatever the surrounding details may be, Razer's mice usually deliver the goods when it gets to the nitty gritty.
For the Abyssus we weren't too worried about the 16 entry limit on macros — yes, it was a token effort, but the Abyssus is an entry-level mouse, with the macros essentially tacked on as an extra feature that the end user would likely never use.
Considering the cost, the Imperator is a more serious beast, and the macro limitation hurts it, leading us to suggest you look to other gaming mice in the same price range. Perhaps the upcoming 2012 edition will address this — we look forward to seeing what Razer has for us then.