It's good because it's a very successful commercialization of .260 Rem, which is a natural adaptation of the .308 case to 6.5mm-- which itself was a good idea because of the historic success of 6.5x55, 6.5-06, etc. It does not have the case capacity of 6.5x55 or 6.5-06 or 6.5-284, or any of the magnums, because it is a regular 308 sized cartridge designed to fit into normal 308 rifles.
I have competed extensively with .260, and tested it vs. 6.5CM, and these work great. 260 vs. 6.5CM comes down to availability of commercial ammo and the best components. 6.5CM and .260 are great long-range competition cartridges because of the 140-grain class high BC match bullets available, the ability to launch them at a reasonably fast velocity (2750-2900 fps depending on load and barrel length), and a pretty decent barrel life (over 4000 typically). These days match guys who don't care about barrel life (or power factor) are shooting a lot of 6mm's (6XC, 6 Creedmoor, 6 Dasher, and others). For longer range matches, or where a single round's hit is worth more, 6.5 PRC is a popular choice.
6.5 Creedmoor, just like 260, 6.5x55, etc, and all those, is a good all around hunting cartridge because with good bullets you can shoot the largest N.A. game, and for normal game you can shoot just about any bullet. It has longer barrel life than .243, but supports a heavier bullet, which is useful. It's good for deer sized game for the same reason 257 Roberts is.
In some sense, the best argument FOR 6.5 Creedmoor is that it was marketed successfully by Hornady, who basically made a "good cartridge idea" (that, yes, had been reincarnated in at least a dozen similar cartridges over the last 120 years), ubiquitous in modern rifles and in modern applications.