I went to 12s XTR a few months ago. First xtr I've paid for in many years. It's outstanding, and i only did it after giving up on GXX warranties and the hassles that come with gX jockey wheels lunching themselves when you're back country. I've found the shifting (even with an eagle chain on a praxis ring) amazing, and the brakes the best I've ridden.
Like loads of SRAM stuff, some people have great experiences, loads have shocking ones - that inconsistency in QC is the real problem.
Being able to set up and tune without a sagged bike and a ridiculous piece of plastic is nice too.