The new maps are a bit shaky, and very road-centric. We got lost wandering in the woods near Robertsbridge yesterday and our usual escape plan in such situations is to use the GPS phone to figure out where we are on the OS map. This relies on there being common landscape features like woods, streams, etc. Apple maps just has roads and not even lanes. As there were no roads nearby, that wasn't terribly helpful. Google came up trumps, since the data is far richer, and we could align the woods and streams between Google and the OS map. So we arrived back in Robertsbridge before the night fell and the zombie squirrels emerged.
So, yes, you can use the Google maps web app, and it'll do GPS and most Google maps features other than street view. Bear in mind that all apps that use maps data use the Apple equivalent now.
I'm also sure Google will get their own native iOS app for maps. Also, the Apple map data will improve. Google have the headstart, of course.
Other than that, the upgrade seems to have gone mostly* smoothly. Nothing ground breaking but lots of pleasing little features to stumble across. Some are about-times, others actually quite cool.
*My iPhone refused to sync with iTunes. Some Googling later that turned out to be caused by the fact that I had a few voice memos on my phone that I had to (apparently) delete. It's 2012, Apple, so please say no to the iTunes cryptic error codes.