There are so many things I like about the M90! The LED lighting is well placed and just enough to look classy without distracting you in your peripheral vision. I like the grip on the right and the sunken in area on the left that allows you to get a good grasp on this mouse as you swing it around in the heat of battle. I was able to map the buttons to all sorts of things in the game and the macro functionality was as easy to go through as it was with the keyboard.
This software is very intuitive and it makes things easy for someone like me who never used macros until I reviewed devices that had that feature. Lastly, with the on-board memory and the fifty profile potential on the mouse, I like that I can take it over to a friend's house and have my settings go right along with me, so I don't ruin my KDR learning someone else's products.
There is one major issue with the M90 for me personally and that is the fit of my hand to the mouse. I don't have enormous hands (7.5" from wrist to the tip of my middle finger) but most mice seem to fit in my hand pretty well. With the M90 it was a two-fold issue. In order to get my thumb to reach all of the buttons on the left side of the M90, my fingers had to hang a full digit over the front of the mouse. That in itself wasn't so bad and I could deal with that if I needed to, or could. The issue was in order to keep may hand in that placement, my arm had to be raised, because the slope of the back of the M90 sort of forces your hand to slide downward on the back and this makes the buttons on the side about half to three quarters of an inch too far forward to be comfortably functional in a gaming situation where speed and gut reaction time is what makes the difference between a kill and losing a set of dog tags. I was able to shift the functionality of the main features of the mouse back into a reachable area for me, so at least it wasn't a complete wash, but I did not end up using two buttons on the side.
Even with the fact that it wasn't a perfect fit for me personally, there are many sizes of hands out there, I am just warning those with a short span across their hands this mouse may not be what you are looking for. For those of you who like a well designed mouse with a bit of weight to it and of course the really sleek look of aluminum and LEDs done just right without getting gaudy, this mouse is for you.
To be honest, even with the irregular fit to my hand, I found myself gaming on it for two solid weeks and that is saying something! I have plenty of other mice around the house to use and to continue using something for its functionality over a perfect for me lends so well to the superior design and effortless use you have when the Vengeance M90 Performance MMO and RTS laser gaming mouse is plugged into your PC. For the asking price of near $80, I have had other mice that have come and gone that fit my hand much better and for a guy who couldn't keep his hand on the mouse correctly to still enjoy its use and somewhat limited functionality due to my short thumb, totally proves that even if not exactly for everyone, Corsair still did a terrific job with this mouse.