I drove a G80 3.5t and a G90 3.3t back-to-back today. With regard to this thread's topic: "Anybody go G80 to G90? Was it a nice upgrade?"
Yes, it's a
huge upgrade. The G80 is a competent luxury car. It's pretty quiet, has a comfortable suspension which does a good job of absorbing road imperfections, and has good tech. But the G90 is 95% as good as the Mercedes S Class, BMW 7 Series, etc. (I've driven both of those). It's much quieter and noise from the world around you is blocked out more effectively. The suspension is much better at deleting road imperfections. And maybe I'm just weird, but when I got into these three big luxury sedans (G90, S class, 750) I felt calm, relaxed, and at peace - even from just sitting in them for a few minutes. The G80 doesn't do that at all for me. Even the BMW X7, which in terms of materials and comfort and quietness is very close to the 7 series sedan, doesn't do that for me. I don't know what sort of magic they use when designing these sedans to make them feel this way. Also, in person the G90 looks much more substantial/important compared to the G80.
The 3.3t in the G90 impressed me. I'm sure it's not as good as the 5 liter V8 - I'd say it felt a bit worse than the V8s in the BMW 750 and the S class. But it still pulls the car along fairly effortlessly and doesn't make excessive noise from normal driving use, and you never feel like the engine is being stressed. It fits the character of the car fairly well - but again, the V8 would probably do that even better. The dealer I went do didn't have a V8 G90 in stock, but I was completely satisfied with the 3.3t which is not what I was expecting.
The 2021 3.3t AWD Prestige G80 is $69k. From what I've heard about the upcoming 2022 G80, to get the 3.5t engine (weak 4 cylinder engines absolutely do not belong in luxury cars IMO) and all other the good features/tech that's available, Genesis will force you to get the G80 Sport, which will be around $72k. The 2021 3.3t G90 the dealer had was $75k; the Genesis online configurator says a 3.3t 2022 G90 will be $77.5k. For such a minimal $5k price difference, I think it's a no brainer to go for the G90 over the G80. Unless the larger size won't fit your requirements or you really want the refreshed design right now.
There are only two issues I observed with the G90:
1) The 7 series / S class almost delete bumps and potholes in the road. The G90 doesn't have air suspension but is still very good at giving a comfortable ride. However, the suspension does still make noise when going over bumps - you don't feel them, but you can still hear them a lot more than you would in a 7/S. Maybe there was an issue with the specific car I drove? Can't remember how the G80 compared to the G90 in this aspect - I drove the G90 first, and it was obvious to me shortly after starting the G80 test drive that the G80 was much worse, so I didn't pay a lot of attention to the G80.
2) The AC is not very effective and thus needs to be turned up to higher fan speeds, creating noise. The seat ventilation is also pretty ineffective and quite loud. The G80 is even worse at both of these.
But at $75k vs $110k minimum for the German cars, I think the G90 is the obvious choice in this comparison as well.
I also drove a Lexus ES300h today. It's less than $55k fully loaded so I wasn't expecting amazing performance, and it is much worse than the Genesii - as RonL said it would be. But it's a big step above my current Honda Civic and is still very tolerable to drive. I'm probably going to buy that, keep it for 2 years until it's 'safe' to buy the refreshed G90 for the 2024 model year in fall 2023 (I don't like buying the first model year of new designs), then give the ES to my family and get the G90 at that time. Also 43/44mpg city/highway is nice

- efficiency is one area where Genesis/Hyundai could use some serious improvement.