By many accounts, Apple's new Maps app, which relies on data from a variety of sources like TomTom, Waze, and Yelp, isn't as good as the current app that uses Google's data. Even Walt Mossberg said Maps is the one of the biggest drawbacks in iOS 6.
I've spent some time with the beta version of the new Maps app and I also found this to be the case. Specifically, the new Maps app is missing built-in public transit directions, which is a huge problem if you live in a city. (Apple will let third-party transportation apps integrate with the new Maps, but that means you have to hope a third party developer cares enough to include your city. Plus, it's really annoying to download another app just to get transit directions. Ugh.)
...it's missing Google's Street View.
...Yelp's venue search isn't as good as Google's.
...if you have an iPhone 3GS or iPhone 4, you can't access those super cool 3D maps Apple added.
...if you have an iPhone 3GS or iPhone 4, you can't get real-time turn-by-turn directions.
Bottom line: With iOS 6, Apple is making one of its most popular and most useful apps worse than it was before.
In the meantime, we have to hope Google decides to bring Google Maps back to the iPhone on its own with a separate app you can download in the App Store. Unfortunately, Google hasn't committed to doing so yet.
Will it get better? Yes! Definitely. Apple and its mapping partners will continue to improve stuff over time. But in the near-term, you're getting a worse mapping experience on your iPhone and iPad than you had before, which is antithetical to everything Apple stands for.