Before the iPad was announced I did a little thought experiment. I asked myself, "What's the easiest way Apple could develop something that could be considered a tablet?" The thing I thought of had a 7" display at 480x720, was half an inch thick, and had a base model with 16GB at $499.
The display I plainly got wrong. I arrived at it under the observation that both the imagined iPad's 480x720 display and the iPhone's 320x480 display would share a side with 480 pixels. The imagined iPad's width would be the same as the iPhone's height. Imagine taking Mobile Safari in landscape mode and then just stretching it vertically to fit 720 pixels instead of 320. Imagine the portrait keyboard on the imagined iPad being the same size as the landscape keyboard on the iPhone. Under this display, the imagined iPad software could literally be nothing more than scaled up iPhone software: the exact same toolbars, tab bars, and navigation bars, just with larger content areas. Toss in an eBook reader, and I felt that you would have a legitimate product, albeit one that would have serious differentation issues against the iPod touch.
That was the product I arrived at, and I would call that the bare minimum. I seem to be the only person who had their guess exceeded by the actual iPad. With a 1024x768 display, they couldn't just have the thing literally run iPhone software with scaled up content areas, they had to go beyond that. They introduced new UI concepts in the form of split views and popovers. Some iPad software—like Notes—is only a little different from its iPhone counterpart (Notes basically took the iPhone app and added a split view in landscape mode), while some software—like Calendar—has been completely rebuilt. They added the requisite eBook reader, but then went beyond that and ported iWork.
So, my assertion is that the iPad isn't quite the bare minimum it could've been. It could have been a smaller device, without iWork, and that literally ran all the same built-in iPhone software, just stretched to fill more space. It's still pretty close to the minimum, though, so I can respect that people are underwhelmed by it.
Just a fun point, I had shared my little imagined product with my coworkers before the iPad announcement. As time went on during the announcement and we found the thing exceeding my prediction, we started thinking my price estimate was too low. "There's no way this thing is gonna be $499," I said, "it's gotta be more like $700." A coworker guessed $799-$899. Then Apple announced $499 and we all stood there silent for a moment, "... wow."