The iPhone 12 reviews are coming in today. It seems there are a few points most reviews have in common:

They dig the new industrial design. (Me too!) Matt Panzarino calls it, “the most premium feeling piece of consumer electronics I’ve ever touched.”
The jump from iPhone 11 to iPhone 12 is a more significant step than iPhone 11 Pro to iPhone 12 Pro. I suspect the iPhone 12 is going to be very popular.
It sounds like the iPhone 12 Pro Camera is better than the 11 Pro camera but not the quantum leap we got last year. Maybe that will change once people can start using the bigger sensor in the iPhone 12 Pro Max.
5G isn’t a thing yet, and the tests are confirming that. I’m glad Apple put 5G phones in these new iPhones. iPhones stick around a long time, and 5G will be a much bigger deal in a year or two, but I doubt it will make a difference in the immediate future.

If you want to read just one review, I’d recommend Matt Panzarino’s TechCrunch review. If you are smarter than me and want to avoid the deep dive on iPhone reviews, Chance Miller at 9to5Mac did a great job summarizing them.