As mentioned in my initial post, I'm approaching this review with a very low bar to compare against. I also made my comments on unboxing and initial setup of the mouse, its firmware (yes really,) and software in my initial impressions.
With that out of the way, my longer thoughts...
I hold my mice in a palm grip, and the Sensei felt incredibly comfortable to hold, with the extra grippy rubberised panels on each side giving my plenty of grip for fast movements. It's slightly lighter than my old mouse, and combined with the increased sensitivity of the sensor and the excellent non-stick pads on the bottom the net effect initially was both my hand and my mouse pointer overshooting their mark by some distance. It was about a week of daily use before I got used to this, and now it not only seems natural but a huge improvement on my old mouse. As an acid test I plugged my old mouse back in.
My. God.
The lack of precision was like trying to write while wearing mittens. I can't go back now. If you've never used a gaming mouse or have a very old mouse I'd highly recommend the upgrade, even if you aren't using it for gaming. The improved sensitivity and precision can only help your productivity and possibly reduce the strain on the ole' carpal tunnels.
Now, to gaming. The big selling point of the Sensei is the 1:1 correlation between your movements and the mouse pointer as a result of the enhanced sensor. They don't claim to magically make you a l33t g4m3r, as their video says "if you suck, you'll still suck" but I found I sucked LESS than I used to. In Battlefield 1 I was dying just as much but getting more shots on target and controlling recoil much better. I even managed to snipe someone, which I've never managed before (I did say I suck!) using the button behind the mousewheel that allows you to toggle to a lower DPI setting for just that task. It really does work, as do the extra programmable side buttons if you remember to use them.
Therein lies the rub, once I stopped making a conscious effort to use the DPI toggle and side buttons for testing purposes I forgot they were there and virtually never used them again. The way I hold the mouse the side buttons aren't in the way so you won't press them by accident but they may be a wasted feature if you don't make the effort to learn. As an ambridextrous mouse it has two buttons each side, but you're likely to use only the two on your thumb side as the others will be difficult to reach.. The right hand only version of the mouse deletes the off-side buttons so I assume that is intended but if you do have a freakishly long pinky then you'll have extra options here, as I'd imagine you do in all sorts of other areas.
I was correct in one part of my preview: I've not been back to the RGB settings in the Steelseries Engine app. It's on the default colour cycling program but it's not as garish and GAMERZ ARE HERE as I thought it might be. Unlike some other gaming mice it actually looks like a mouse rather than Optimus Primes codpiece so full marks for restraint there too.
To sum up, a brilliant mouse with a great sensor, comfortable hold (if you're a palm gripper anyway,) easy to use software and relatively subtle RGB. I'd heartily recommend it for anyone upgrading from an old/low sensitivity mouse and the price seems fair given the competition. Just bear in mind you might not need all the extra buttons and if you can forgo the RGB as well you can probably get away with their cheaper Rival 110 which uses the same sensor and software.
Finally, I did check. Yes, it can play Crysis.