I am very happy to see the improvements in Cougar's products. I tried their first mice back in the day, and I cannot even compare them to their newer ones. They have listened to community feedback, realized their earlier mistakes and started releasing actual top-tier products.
The choice of materials is good, and I like how it feels in my hand, but would probably change the side coating to something more grippy. This honeycomb-like design can get quite slippery if your hands tend to sweat a lot. The build quality is absolutely great, no squeaking and no creaking anywhere, only a tiny rattling noise caused by the CPI-switch, but even that only surfaces when one shakes the mouse really hard.
The sensor is quite flawless. Its implementation great, so it should not let you down in an important moment while in-game, be that a very hard bossfight or an insanely close FPS match. The smoothing on and above 2100 CPI is almost negligible, but I would suggest staying below that value if you want to maximize performance. The 2000 Hz polling rate is something I did not really like because of the graphs, but it didn't feel off in-game at all, so I don't see a reason why it shouldn't be used.
There is always room for improvement, but the main buttons are already in the "good" category. They don't have any notable pre-travel, but do have a little post-travel, which could be a downside if you spam your buttons really hard. The scroll wheel is great; the Alps encoder is very durable and has great, tactile feedback. I would be happily astonished if the scroll wheel and side buttons would all of sudden use some higher quality switches, but honestly, they do the job just fine. That room of improvement mentioned earlier is a bit more spacious here, though. All in all, compared to many more expensive mice out there, these buttons are pretty good.
As for the cable, it's a bit thick, but rather flexible, and it's not braided. It doesn't generate much friction if you drag it across your mousepad either, but I always suggest getting a bungee or taping your cable in place. The feet are quite good; they were not misaligned and did glide smoothly. Their friction could be slightly lower, but you can always go for high quality aftermarket ones if you want to maximize this aspect.
The software is absolutely not bad, but I think it could be simplified a little bit. It's rather lightweight and shouldn't affect performance while running in the background, but if it does bother you, you can uninstall it because the 512 KB of built-in memory will store all your settings.
The RGB lighting options are many, look nice and transition smoothly. Both the scroll wheel and Cougar logo at the back light up and are programmable independently from each other, which is a cool feature. Of course, you can turn all of these off if you don't like the eye candy part.
There really aren't many mice out there with a similar shape besides the earlier Minos editions, and the X5 surpasses them all in pretty much every aspect. This is definitely a mouse I could and would play with, but my main one is just a tiny bit more comfortable for me.