The biggest weakness of any mobile gadget is still battery life. True it's gotten better over the years, but that's because hardware has become more energy efficient, not that battery technology has gotten any better.
In addition to hardware improvements, software developers are coming up with tricks to improve battery life as well. Apple's new iOS 9 gives most gadgets hours more battery life than iOS 8, and Google's new Android should do the same.
Android 6.0, Marshmallow, includes a mode called Doze. When Android senses the phone or tablet isn't in use, it stops all activity aside from some basic message checking and syncing. In other words, when your gadget is just sitting around, it will barely sip power. When you need to use it, you'll have plenty of juice to burn.
That's a nice addition and Google wants to make sure everyone gets it. In the past, gadget manufacturers have been free to mess with everything about Android. That sometimes leads to them disabling key new features, or making them not work as well. This time, Google is having none of it.