The real mark against the 600 EX-RT is that you can not use a radio transmitter in the mix if you are also using optical units like the 430 EX-IIs and 580 EX-IIs. The 600 EX-RT can control these units, but everything has to be fired optically so you cannot use the radio to fire units around a corner or in a soft box while using the other units in line of site. Everything either has to be radio triggered or optical triggered. Unless you have the budget to replace all of your older units you will still be locked into optical triggering for the unit.
The 600 EX-RT comes with to CTO gels and a gel holder, this is a nice addition to the flash unit as it makes it quick and easy to change gels. I suggest using one of the CTOs to make a template that can then be used to cut gels for the other colors you shoot with.
All in all I find this to be an exceptional unit, with the added benefit of a radio trigger which would ideally free you from the need to use Radio Poppers or some other radio triggering method. Unfortunately in this regard it does fall short in execution.