Luke’s lecture to Jess was fantastic. It's fun to watch Luke go from being a cheerleader of the Rory/Jess coupling to the paranoid guardian in a matter of minutes. I imagine that having skipped the formative years of raising a kid it’s harder to just let it be as Lorelai was doing at the end of the episode. Of course, imo, he’s justified to be suspicious but nonetheless it’s endearing.
It's sweet in a way that Luke is protective of Rory, but he takes it to an extreme with all of her boyfriends. He's like Richard in this way (except with Logan), but Richard has the excuse of being her grandfather. Luke genuinely likes Rory, but his excuse is the wanna-be lover of her mom. He's an agent of goodness here but it often seems weird the way he looks at her with boyfriends, starting with Dean, as though she's a Virgin Goddess or something. Of course it's different that his not-to-be-trusted nephew is involved this time, so that is a factor.
Luke was pro-active where protecting Rory's virtue was concerned, but he was reactive where Jess' education was concerned. I notice this difference in the way Luke treated two situations where Jess can't be trusted. He always feared the worst about Jess and school but never seemed to find out the ugly details until it was too late. He made efforts before he shipped Jess back to NY, such as the tutoring idea, but this time around it all seems to be on the faith of Jess' word. The sad part is that even if he was pro-active about Jess it wouldn't have mattered because Jess was going to do what he wanted. Maybe deep down Luke sensed that Jess' education was beyond his help, but with Rory-Jess he felt he could exert some kind of effective authority (which didn't have much effect either).