I held off upgrading my 3G to iOS 6 specifically because of the Maps debacle, so this was generally good news.
Turns out that, since it's a 3G, both talking directions and 3D view don't work at all in Apple Maps. There's no good reason for that, as far as I can tell (other than to get you to buy a newer phone), but it also means the issues with wonky 3D views that have caused so much glee at places like http://theamazingios6maps.tumblr.com/
don't show up at all for me.
Biggest difference that I've seen is that Google Maps will actually furnish transit directions. It'll look around for the nearest rail station when you start asking for directions, and if you want to go a really long way without driving, it's even got Amtrak schedules in it, so things like "200 Riverside Place, Chicago, IL, to Starbucks, 200 Public Square, Cleveland, OH" produce actually reasonable directions. None of this "Walk 694 miles" nonsense. And, it even looks nice.
Apple Maps just brings up a pane where you can download a different app for transit directions, which is just lame. I don't even see why they bother having the button for transit directions in there, if they can't provide them.
Otherwise, yes, I'll agree that the Apple Maps is probably fine for a lot of things, and I hope they get all of their well-documented data problems fixed, but until then, it's worth getting both apps installed.