It was a couple of years ago for me when I moved from Axe FX II to Axe FX III that I got the biggest surprise. It might not be a feature that anyone would be thinking about as such, but at the same time it's the most "core" feature of any in all amplification for musical instruments, particularly tube guitar amps.
I had thought that the last iteration of Axe FX II firmware "edge of breakup" tone and feel on cleaner amps, and Factory IR sounds were about as good as modellers were ever going to get. Definitely good enough that I wouldn't be buying many more real amps and cabs.
The Axe FX III was a massive surprise for the improved feel and sound of those models, and since then the simulations and interfaces (front panel GUI layout/Axe Edit) have improved incrementally so many times - one day I must set the Axe FX II back to where I started in 2016, or whenever it was, and compare it with modern day Axe FX III models. It has been quite a journey, and it really is hard to imagine the blood, sweat and tears the Fractal Audio team have ploughed into the last few years. Just in case any of them are reading this - a lot of us really appreciate your efforts, you have been amazing and I'm sure you will continue to be. The first surprise was the way your products changed the way I think about modelling amplifiers, but the last few years they have changed the way I think about everything guitar related.
Second biggest Axe FX III surprise? Well it involves another purchase, but FC controllers. Come ON! A new era when I got my FC-12.
Liam