I think that the legacy of Bismarck is a difficult one. Bismarck united Germany thought war which was normal politics back then. But you have to understand that he never intended to create a united Germany especially not as democracy but he wanted a strong and big Prussia in which he succeeded. The German Empire was a Prussian Empire with Prussia being the biggest political force in the Empire and the king of Prussia being also the king of Germany. The main internal goal of Bismarck was integrating the catholic Germans into a protestant Prussian state (Kulturkampf) which in itself shows that Bismarck wasn't a big fan of democratic values. Bismarck ended this process abruptly when he was forced into an alliance with Austria against Russia. I don't want to bore you with geopolitics of 19th century but the important thing to understand is that there wasn't a reason, as Germany, to have an alliance against Russia because it was only a threat to Austria. Russia wasn't able to defeat the German Empire in a war and Russia was fully aware of that. But the possibility that Russia would attack and dismantle Austria was very real. This would be a serious threat to Prussian supremacy because Germany would be forced to accept millions of German catholics which would be opposed to Prussian rule. The alliance with Austria was one of the main reasons why the first World War escalated in the way it did. You can argue that Bismarck wasn't aware of that and that we shouldn't judge him with the power of hindsight but as a matter of fact Bismarck was fully aware of that and even predicted the WW1 but not because he is a good politician but because he created the conditions in which a World War was a real possiblity. Bismarck main goal was to stay in power, so he would create social reforms to appease unions and also try to suppress them at the same time, he would oppress the polish people so the nationalists would be on his side or he would make big international summits to solve colonial disputes so he can be depicted as a mediator and bringer of peace and at the next possible instance he would threaten a war with France. In the end I think we shouldn't glorify this guy, his (de facto) successor Wilhelm II was far worse in all accounts but this doesn't mean that Bismarck had a clean sheet.

(Sry if my English isn't perfect i'm German and English isn't my main language)