i know use Guitar Rig since version 1 many years ago and i also got Guitar Rig 5 with my Komplete 8 and 9.
It evolved greatly but i rarely going to use it these day to play through it. in my opinion the sound is pretty good and solid, especially the latest added Amp Models like the already mentioned VAN51 and Soldano, i dug those alot.
Also lots of effects are including which sounds great and inspiring to me.
I do use on it some tracks occasionally that were recorded and just send out the DI Track to an instance of Guitarig to add a different texture or blend to the original recoreded track.
And i use it regulary for Bass.
It makes a huge difference which kind of DI Input do use, as it does for most ampsims