Didn't care for it
I might be in the minority but I just finished watching it and felt this movie was slow and long. IMO that doesn't equate to a "thinking film". Lucien was a dickish piss-pot, nothing connectable for me about him at all, I liked Albert much better and he wasn't all that likable either. When a movie's main protagonist ends up being unlikable it makes for an unwatchable product.
Nor did Lucien have a lot of dialogue or emotion, and except for the laughing at the end I felt he was very stoic in everything. First part of the movie it was like he was just following everyone around and soaking it in, yet afterward little to no action out of the main character. Can't blame the actor really, it seemed to me the writing was just bad. My favorite characters were probably Albert and Lucien's mother.
Saw another film a few weeks ago set in WWII German-occupied France, "Au Revoir Les Enfants" (1987), and I felt this was so much better than "Lacombe, Lucien".