Quick reviews of Harper records for almost 10 yrs as PM
http://www.cbc.ca/news/politics/canada-election-2015-harper-political-obit-1.3273677
I think Steve-o biggest mistake was reduced the GST by 2%. 2% cut translates to reduce 14 billion annually in revenue according to the article.
If he has not do so, we probably has more than 3 yrs of surpluses.
One thing I will give our former PM credit is that when he promised about cutting taxes, he delivered. However, these tax cuts or credits mainly benefit the wealthy or for the people the fairly financially secured that do not need these tax breaks.