Was Peter the Great really great? Why or why not?
He was, for making Russia a European power for the first time in its history.
Russia spent the last 200 years of the Middle Ages as a vassal state of the Mongols, and spent much of the next 200 years getting humiliated by Sweden, Poland and Lithuania (which is unthinkable today, but those were formidable military powers in the 17th Century). Russia, though a large land mass, was a rural backwater and largely ungovernable.
Peter I was, unlike his predecessors, oriented more towards Europe than Asia and the Middle East. His visits to Paris inspired him to drag Russia fully into the 18th Century. He built a new city on a Baltic inlet, St. Petersburg, with the intention of rivaling Paris. This gave Russia a naval port with access to the Atlantic, something Russia had never had before.
Culturally, he brought Russia closer to a European style than it had ever been. He made his nobles, the Boyars, shave their beards and dress in Western clothes instead of the Mandarin finery they were accustomed to. And he made Russia a naval contender in the Baltic, which it had never in its history been before.
He brought Russia from a remote tsardom to a European empire (he was Russia's first actual emperor).