NS is clearly popular with SNP/Yes voters and those in the rUK who, with respect, have only a superficial knowledge of her & her party's policies.
She's compared favorably to Alex Salmond, however was part of a leadership team who orchestrated a bitter and manipulative "once in a generation/lifetime" Referendum campaign, which set friend against friend and divided families. Who invented agreements on EU membership and the continued use of sterling. Who grossly exaggerated oil revenue estimates and projected GDP on a best-case scenario, with no regard for the potential downside of leaving a Union on which c.65% of Scottish jobs & trade depend. In short, she attempted a massive confidence trick on the Scottish people.
She still purports to act in Scotland's best interests, yet is committed to the ideological ‘Full Financial Responsibility’, which independent experts have calculated would cost Scotland a minimum £8BN per year (by comparison, the "swingeing Tory cuts" would equate to less than £2BN and our share of any Trident replacement c.£0.2BN).
This would normally entail massive reductions in public services &/or tax increases. However NS contends that a fiscally-autonomous Scotland would magically grow at a rate of over 5%, roughly twice that of any developed country!
Voters would do well to consider this economic track record when evaluating her proposals for a "modest" £140BN increase in UK spending.
As others have touched on, her quest for power has seen SNP numbers swelled by many from the darker side of democracy, the aggressive harassment of Labour's Jim Murphy being the most recent example.
This can be added to a charge sheet which includes Cybernat online abuse of anyone holding opposing views, patriotic 'No' voters described as traitors, attempts to intimidate the BBC and perhaps most disgracefully, the First Minister's toleration of parliamentary candidates who've made anti-elderly and sectarian comments.
Scratch the surface, as occasionally occurred in the Scottish Leaders' debates, and you'll find a less palatable personality.