The Define R4 is designed as a quiet PC case, and yields a huge sound reduction compared to non-quiet PC cases. It is comparable to other good quiet PC cases, like the Antec P280.
IMO, the R4 is like a budget P280. Having both, here's what I didn't like about the R4 compared to the P280, in order of importance.
The R4's build quality isn't as good. One of the holes for the motherboard standoffs wasn't drilled fully, so I had to enlarge the hole to get the standoff in there.
The R4's bottom air filter slides out the back of the case and is very long, and thus is usually inaccessible without sliding the whole case out away from the wall. The P280's bottom PSU air filter slides out the side, and thus remains accessible without having to move the case.
The R4 isn't as tall, so there's less room between the PSU and motherboard, making it slightly harder to plug/unplug cables once the PSU is in place.
The R4 doesn't have nearly as much open space on the back for air to vent out in a positive airflow application.
That said, the R4 is still a very good case, and if you're looking for a case that's smaller than the P280, or that offers more fan placement options, you can't go wrong with the R4.