The N95 is a great example because the internals were superb, but the software was just so poorly conceived. S60 started in the wrong place and the more they worked on it the less it seemed like making it remotely usable was a priority.
The noise from Symbian at the time was that Nokia would get a new chip in and then come up with some lunatic scheme that involved using all the new CPU power in the stupidest way possible, causing newer versions to have even worse performance over time.
Their lunacy wasn't confined to S60 ( https://en.wikipedia.org/wiki/Nokia_3650 ), they also released madness like https://en.wikipedia.org/wiki/Nokia_7600 . It's no surprise that during this time SonyEricsson started making serious inroads on them with things like the https://en.wikipedia.org/wiki/Sony_Ericsson_K750