And the biggest shortcoming:
No major companies (ie cash, marketing and lawyers) promoted/backed BeOS. BeOS was betting on next generation Apple OS. When that did pan out MS killed BeOS by scaring PC vendors threatening to jack up rates on Windows if BeOS was offered as a boot option.
Well... Yes and no. Those were definitely contributing factors, but not the whole story. To add some detail to those points:
BeOS did pretty well in the retail market, with R4.5 (IIRC; may have been R4) outselling boxed copies of RedHat for a couple of quarters. Agreed re: not having the level of promotion others did, but it was receiving very favorable press which in many ways was almost
The next-generation Apple OS: what nuked that was Jean-Louis Gassée overestimating how much Apple was willing to pay for the company. By buying NeXT, they got Steve Jobs into the deal and for less money. Spend half as much and get the guy back who actually knows how to run the company? It was a no-brainer.
Strangely enough, that leads into why Be ported the OS to x86, and why Microsoft later strongarmed hardware manufacturers into keeping Be out of the bundled-OS marketplace: after the NeXT acquisition, Apple suddenly weren't interested in cooperating with Be as regards technical information necessary to port the PPC version of BeOS to the G3 architecture. Be went to x86 as a result, and... Despite (or, depending on how you look at it, because of) massively increased interest in and uptake of the OS as a result, they still got screwed.
The one that really sunk them, though, was the focus shift from BeOS to BeIA.
For anyone unfamiliar: BeIA was the Internet Appliance platform derived from (but not binary-compatible with) BeOS. They basically bet the farm on Internet Appliances being the next big thing, and it was a bad bet. Development on BeOS pretty much stopped as soon as the Compaq Clipper and Sony eVilla were in the picture and being actively developed for, so the parent OS was effectively dead (which also explains - in part - why R5.1 never saw official release). However, once it became apparent that nobody wanted a $99 email and web browsing terminal that forced you to subscribe to at least a year's dialup service at inflated cost in order to use it, the writing was on the wall. It did not take long for this to happen.
Anyway my brother still runs a local radio with Tune Tracker. He has an over 2 decade old BeOS PC and spares / parts that STILL runs the radio station to this day. Much much cheaper and less issues than even current Windows solutions: http://tunetrackersystems.com-- currently sold with HaikuOS .
TuneTracker is a pretty damn awesome piece of software. But if there's one thing in BeOS that I really, Really, REALLY miss, it's Replicants. Being able to basically shove data from any application to any other application completely seamlessly was so damn useful at times.