If anything, "promising" may be the wrong choice of words because it was arguably better and more mature than the equivalent debut iOS and webOS devices at launch. Of course that's cheating a bit, as the tech stack had some history behind it by that point. Still, for a line-incepting product it was very impressive execution, especially for a company that was still so hung up on a legacy product line at the same time (Symbian).
Personally, I used one as well and I don't find it very hard to imagine a version of the world where it could still be my preferred OS/ecosystem right now. It was truly a strange situation, and Nokia of the day one strange animal of a dissonant company. I don't know if Nokia would have made it without the MS interference -- but I think it didn't help.
This is a nice little nostalgia anecdote too that gets discussed on HN occasionally: http://nition.momentstudio.co.nz/2014/08/the-nokia-n9-alarm-...
"Promising" is an interesting choice of words here.