When Mormonism was being founded local newspapers were highly critical of the new religious movement and Joseph Smith, but what exactly were they saying about them?

You can see some of them for yourself here:

https://user.xmission.com/~research/early/news.htm

But generally, they spoke in a very broad, sweeping, generalized nature, asserting that Smith and Mormonism were obvious frauds. This quote from the New England Christian Herald, on November 7, 1832 (2 years after Mormonism's official founding) is illustrative of the tone and sentiment:

We have before noticed the bare-faced and outrageous delusion abroad in the country, under the name of Mormonism; and though it is so shocking to common sense, to reflect upon such a silly, and egregiously absurd, though wicked system...

To understand these statements, it helps to understand their context as part of the Second Great Awakening. Western New York (where Smith lived) was particularly swept up in the movement. So much so that it came to be called the "burned-over district" because of the highly publicized revivals that crisscrossed the region. This intense competition among religions led to Smith's interest in religion and personal quest for answers (according to his own retelling). But it also led to fierce criticism of him and his burgeoning sect as feared competition in this fiercely combative environment. Many newspapers of the time were religiously affiliated.

For further reading I recommend this article discussing shifting popular treatments and images of Mormonism:

http://www.ijmsonline.org/archives/1512

I also recommend the book Viper on the Hearth by the same author, which examines anti-Mormonism in the 19th century.