Here's the thing, I will not be speaking about the sensor at all. It seems that all current 8200DPI mice are using the same Avago ADNS 9800 laser sensor, and I will sum up my opinion on it in a simple paragraph and move on to more important bits and bobs.
The sensor is not great for gaming. If enough tweaking goes into it, many of its hiccups may be fixed, but it's still weaker than its predecessor the 9500. Luckily, Corsair has adressed many of 9800's problems, such as jitter and latency, via a firmware update, that becomes almost mandatory for any high-precision fps gamer.
Oddly enough, the buttons are quite stiff, which in turn provides a very distinct and clear feedback on click. It's actually quite hard to press the wrong buttons on the M65 by accident, mainly because they're only 8 of em, but also because the buttons are so rigid.
Day to day use
Just by looking at it, you can tell that the m65 is not for everyone, with its heavyweight build and almost compact form-factor. Using it as a normal day-to-day mouse shouldn't be a problem, but it does take some getting used to. Here's the thing though, this is a gamer's tool. Even if it has that "less-is-more" sleek, stylish Corsair look, it's still a gamer's tool. As such, you will find on the IT enthusiast or PC Gamer (most likely a shooter fan) desk.
The software is capable of providing some shortcuts and since you can assign a profile to a specific application, you could actually build a massive back-catalogue of work-arounds for some of the "not-so-user-friendly" applications out there.
Like the M60 before it, the M65 is and should be seen as a dedicated gaming, specifically shooter peripheral. It uses low-friction teflon feet to glide merrily across the desk. Te rough plastic offers a lot more grip than expected, and the sides seem to be demanding fingers to take their apropriate places. There is this certain level of control that takes some getting used to, until the hand feels comfortable with the overall feel.
Corsair's Sniper button is a welcome addition, a large red button with a distinct feedback, and at the perfect thumb distance (for me, and me alone). It most certainly feels a lot better than R.A.T.'s 9 Sniper-ish button.
I played Metro: Last Light, Firefall and Counter Strike: Global Offensive, and while I will not congratulate or blame the rodent for my performance, I will say that for the most part, it didn't feel like I was fighting with the peripheral as well as the enemy team. I never had one of those "the sensor is going up while I am turning left" moments (the Sentinel Advance II had 10-15 second episodes of erratic behaviour every once in a while) or any serious or visible input lag, which is also a plus.