NT showed promise early on.
I was actually a little excited by what I'd heard and read about the guts of NT---as an old VMS hand a lot of it felt familiar. But I never had a chance to actually use it until the ill-considered decision to move the video drivers into the kernel. I had to warn users every time I needed to make a change to the network user database that was running on one of the company's NT systems---there was a better than 50/50 chance that clicking on "Save" would cause the database application to crash and bring the system down with it. Eventually, we decided that making simple changes like this could only be done after normal business hours. All that solid-as-a-rock VMS lineage wiped out by one silly decision.