tl;dr: In one word, "fun"
I was not familiar with the Lupin character before watching this movie, and while I could tell that there were occassionally things I was expected to know about several characters, it really didn't matter in the end. This isn't the type of anime that you'll feel the need to process and discuss over drinks with your friends just to make sure you've understood all of the deep meaning, but it's not overly silly either. I think the best way that I can describe this move is just "fun." It was a lot of fun.