Like many important historical figures, Peter's accomplishments were often built on the backs of other people. This is true, for instance, of the founding of St. Petersburg, often considered an especially beautiful city, but built in large part by serfs, many of whom died in the process. St. Petersburg has had a very positive influence, in many ways, on Russian culture, but the human cost involved in building it should not be forgotten. Of course, the same thing is true of many great historical achievements, such as the Egyptian pyramids.
In the historical way one can be impressed about anyone who has a strong personality, leadership ability and who made a lasting mark on his country/society. He wasn't a particularly nice guy, so maybe "impressed" is the wrong word. One thing is certain, Russia was never the same when he was done.
On the one hand he modernized the Russian nobility, court life, and to some extent the military. On the other, he actually reversed some fairly progressive trends in Russia, e.g. restrengthening the control over the serfs by the nobility. In war and diplomacy, which were how seventeenth and eighteenth century people generally judged their monarchs, he was pretty successful, capturing a Black Sea port and defeating Sweden in the Great Northern War. Overall, I'd say introducing what was basically an administrative model of kingship to Russia is, in fact, fairly impressive, judging him by historical criteria.
The only thing that I could say was impressive about Peter the Great was his forward thinking about modernizing Russia. Outside of that, I guess one could find his ambition impressive, but his inability to be humble seems to nullify all else.
I don't know about impressed... He was clearly a very forceful person who had a vision for his country. But if he were so impressive, you would think he might have figured out a way to work in a more gradual and sustainable way. I would have wanted him to have opened the country up a bit more and done a bit more for the lower classes. Because he didn't do any of that stuff, I'm not completely impressed by him.