Nokia made great phones during the mid/late 2000s. The N9 was a piece of beauty that continued to have a more cohesive and thought out experience than Android (and even iOS, in some ways) well into the mid 2010s. It was simply a joy to use.
Why Nokia then fell apart might have a little something to do with Stephen Elop and Microsoft, I suspect.
Why Nokia fell apart is because they didn't take the iPhone or Android seriously, repeatedly would say things like "nobody is going to spend $400 on a phone after subsidy", and had tremendous infighting over Symbian, MeeGo, and Windows - tons of engineers and management absolutely didn't want to learn the new thing.
And then, Microsoft, not wanting to pour billions of dollars into what was already becoming a bitter duopoly fight, gave up.
I have an N9 and an labeled windows phone dev kit from post-nokia on my shelf, both devices I used for a year+. They were fantastic.