The 4690K is a 4th generation Haswell CPU, built on Intel's mature 22nm process.
The 5675c is a 5th generation Broadwell CPU, built on an early very 14nm process.
The 5675c include's Intel's "Iris Pro" graphics, which rivals or beats entry level discrete video cards and embarrasses AMD's APUs. The 14nm process allows it to draw much less power than the 4690K, and a combination of a huge level 4 cache and some architecture tweaks gives it a sizable performance per clock advantage. However, the 5675c overclocks terribly, often maxing out at 4.0-4.2ghz, while a good 4690K may hit 4.6-4.8ghz, though both will perform about the same because of the IPC advantages in the 5th gen chip.
Overall, I'd rather have the 5675c, but historically it has been much more expensive than the 4690k.