I have used the G3X extensively live and in home studio. It's an amazing piece of gear for what you get and anyone who dismisses it really hasn't not tried it to it's full extent. If you REALLY want some VERY GOOD sounding tones you can EASILY turn off the cab simulation and either run it into a Lodigy EPSi pedal (this pedal loads SD cards that can be full of the EXACT SAME IR's in WAV format that you all know and love which are loaded into your AxeFX units from OwnHammer, Red Wirez, etc... (and can be easily recalled with a turn of a knob) - Cliff himself has mentioned how important the IR is to the realism of the guitar tone. Or, you can use the G3X with not cab and apply the cabinet using a VST plugin like Sgear, LeCab <FREE!> in your recording DAW.
The unit is also BUS Powered so you can go mobile very easily (I frequently record dry guitar tracks in the back of my Prius using my laptop + G3X) and then re-amp at home. OR you can use the G3X as your audio interface (completely dry signal) and use Scuffham SGear as a VST plugin in your DAW for fantastic studio guitar tones.
This is not to include the fact that the G3X runs on 4 AA batteries in a pinch, sound fantastic in a tube amps loop, has some really great, really EASY to dial FX.... I can go on and on... The ROI (return on investment) for the G3 is unmatched IMHO. Here is a pic of my mobile studio rig and then some clips off of our last EP which is all SGear (~$100?) VST plug in for ALL guitars. All guitar tracks were recorded dry using the G3X and then I applied SGear after the fact. I even did all of the bass lines using the G3X and used Reaper's built in ReaTune plug in to drop the lines an octave for bass