Some of the most significant issues with the iPad have to do with two areas: user management and the Apple "wall"
The first cuts across a wide range of applications from consumer to business. The lack of multiuser capabilities (with permissions and all the things modern multiuser OS's can do) seriously limits usability.
At home I would like to make a distinction between my usage of an iPad, that of my children and that of guests. No, i don't want to buy a separate device for each use case. Accounts for children could have limits set to restrict usage to a pre selected set of apps, time limits, app store settings, etc. Guest accounts would have the ability to setup similar restrictions. A house guest should not be able to open and browse your email, facebook, paypal or whatever.
The same issue applies to business usage. An iPad is a security nightmare in lots of business scenarios. Adding a layer of user management would be a huge step towards fixing this problem. For example, if I use an iPad as a cash register I don't want the cash register user to be able to use any other app. Perhaps i also want them to be able to browse the company website in order to assist customers and that's it.
The Apple "wall" is how I've been descriibing the Apple's control-freak hold on the device and the OS. This goes from the lack of USB and memory card connectivity to the lack of access to a file system, impossibly cumbersome file sharing between apps, totalitarian control of the one-and-only connector (leading to ridiculous hacks such as using the audio port for data communications, something that dates back to the early '80's!).
It's intersting to walk into an Apple store and see the iPads they have locked down to a single app that tells you about the device next to it. Apple themselves understand there are business cases where you need a device that is very tightly controlled, even to the point of limiting it to a single app. They get it. They simply have no interest in letting us through the wall.
Windows and Surface are not and have never been perfect solutions. However, they benefit significantly from your ability to do just about anything you want with them, to connect to and talk to almost any external hardware device in the market and to easily design your own for special applications. You can setup users for your particular needs. You can even install other OS's --replacing Windows-- or simply run them in a virtual machine.
I've come to view our iPads more as toys than as universal machines. They get used for web browsing, playing games and reading eBooks and that's just about it.
I continue to be stunned by how bad Microsoft marketing is. Instead of driving home the point that the iPad is a severely restricted and crippled device they actually spent good money making commercials with people dancing around clicking keyboards on and off their devices. If that's what they trully think is the most significant distinguishing value of their devices they are truly clueless.