I can compare these to at least the X4's for those that care.
These headphones can get really loud relative to the X4's. They put the tuning dial right next to the volume dial so it can be slightly annoying to change the volume and knock the tuning out of it's sweet spot. They do not cup the ear like the X4's and thus don't block out outside sound near as well. In the same vein, they are more comfortable to wear for long periods since the X4's tend to make your ears sweat.
The RS120's only have 1 input option and no output option, e.g. you can't use these as an intermediary between your system and any other speaker option as you can with the X4's which have standard composite sound jacks and optical in and out jacks. The X4's also have built in dolby digital decoding if that's important to you.
As far as sound goes, I believe the RS120's are much better than the X4's for music and casual TV watching. When it comes to sound separation and bass response, they have nothing on the X4's. They can also be used at a much wider range than the X4's which are infrared (line of sight). The newer X41's I believe have switched back to a radio signal and wouldn't suffer from this limitation, though.
These are worthless if you need to use a microphone. These are useless if you are thinking of using them on a portable device as the base is the size of 2 coke cans. I use them as my PC headphones right now as I don't ever talk to anyone on here. If you are into console gaming, you probably should buy a more dedicated pair that has a mic. If you just want a nice pair of general purpose wireless headphones that you may occasionally use for gaming, I would recommend them. Especially at this price.