As disastrous as the Newton was from a business perspective I still look at it with some fondness. It feels ahead of its time in terms of how personal it was to use, but strangely for Apple it was much more complex than the competition.
The Psion range was easier to use, much more reliable and was actually useful whereas the Newton felt like an experiment. Sadly Psion did not make proper efforts to crack the US and Palm only appeared a few years later so in some ways the Newton should have succeeded. I owned one later on for 3 days (bought from eBay) before I resold it pretty quickly. It was, to be frank, awful.
It failed because it was ahead of its time and had to concentrate on features no one really needed, and just perhaps it was the reason the iPhone turned out to be the way it was when released. The Newton was the wayward father of the iPhone which outshone him with ease.