I haven't played with Android Auto extensively, but so far I've found some nice things about it:
1. For me the ability to use Google Maps is a definite improvement over the Kia nav. The ability to touch the little microphone button and say "directions to Lincoln Park" is really nice.
2. The ability to have Google read texts that are received while driving is nice. You can also press the microphone button on the Kia screen and say things like "Text Bob Smith" and Google walks you through this. Not suggesting it's a good idea as it can still lead to distraction...
3. For music, I was given a variety of options, including Amazon Music, Google Music, and a few others.
4. Calendar shows up on the screen, which let's me see what meetings I'm going to be late for
The downsides for me are:
1. It requires that the phone be connected via USB to the car's USB input. This doesn't allow me to charge via my high speed charger (which plugs into the DC outlet, not the onboard USB outlet). Not the end of the world.
2. Phone is locked when using AA. I think this may be good in the long term as it means you're not tempted to check the phone, since it's locked.
3. This has only happened once, but everything lagged horribly for a minute before getting back up to speed (call came in, I pressed the answer button and everything kinda froze up for a minute). Might have just been a one-off issue, but I haven't used it enough to render an opinion I'd trust.