As far as mobile mapping goes, the newest version of Google Maps for Android offers one of the most robust experiences I've seen. More than a simple piece of mapping software, this feature-fest offers turn-by-turn navigation, voice search, indoor mapping (select locations), public transportation information, Street View, and tons of other conveniences. Further, if you use Google Maps on your other devices while signed in to your Google account, your search history, Places, and custom maps sync seamlessly.
When viewing a location, Google Maps lets you activate a variety of add-on layers offering information like traffic, terrain, transit lines, satellite images, and bicycle routes, among others. There's even a Wikipedia layer that I find particularly useful while traveling, as it plots out entries related to points of interest nearby. And if you use your Google account to make custom maps like I do, you can even overlay those on your screen.
If the add-on layers aren't enough, Google Maps lets you zoom into satellite photos to get a close look at buildings and street details. You can even activate street view to get a ground-level look at areas that have coverage. Unfortunately, though, the Google Maps app does not come with 3D flyover images baked in. To get these highly detailed images, you'll have to download it's sister app Google Earth. I don't think this is a huge inconvenience, but I do hope that these two titles eventually merge to offer a more streamlined user experience.
One of the most important aspects of Google Maps for Android is directions. The app lets you easily conduct a search for a destination with text or voice, so you can get directions for driving, public transit, walking, or even biking. I've been consistently impressed with the number of walking paths and bike trails that are viewable through the app, and the public transit directions offer several different options in case you'd rather take a train than a bus or vice versa. Whichever mode of transport you select, you can read your route in list form or hit the arrow icon to activate voice-guided turn-by-turn navigation.
When it comes to routing, Google Maps' navigation usually works well, though I have seen it suggest inconvenient routes in very specific instances. For example, I've had Google Maps route me around the block, when a simple U-turn around a traffic island would have sufficed. That said, I still consider its navigation reliable and I generally trust it to get me from point A to point B. It gives ample warning leading up to turns, and I like that it even gives a warning when you have to make two quick turns in a row. One thing I love about Google Maps' navigation is that it takes into account current traffic conditions when it recommends a route. Of course, if you're not satisfied with your current route, you can always change it midway (it usually offers a few different choices), or you can simply veer off course and have the app reroute you automatically.
Lastly, Google Maps for Android lets you cache maps for access while offline. This is hugely useful for travelers who frequently find themselves in areas outside of their home mobile networks. The feature lets you pinch and drag to determine the area you want to cache, and it tells you how much memory the saved file will cost you.
But more than just a database of geographic information, Google Maps offers other baked-in services like Offers for nearby deals, Local search powered by Google Places and Zagat, and Latitude for locating Google contacts on the map (with their permission, of course). These services in aggregate make for a complete mobile experience that is pretty hard to beat.