The biggest thing I've noticed is Trevion Williams showed up, and then Matt Haarms got good.
My biggest takeaway after MSU beat them in EL, was "well, at least they found their big, because Haarms as the #1 guy has not been good." It seems like once Williams pushed him they went from having no good bigs to two. In November/December they were just whatever Edwards could do. I said they reminded me of 2007 MSU with Neitzel. That he would go full hero, surrounded by a bunch of guys who weren't that impressive, but he alone was good enough to get them middling into the tourney.
Funny thing is now, MSU is more that, with Langford/Ward out. Granted Winston "hero ball" is a little different. Less shooting than Neitzel/Edwards, more keeping the ball for insane amounts of the shot clock.
Williams was a huge boost. If you noticed, when we went into our lull over the last several games (lost at Maryland which you can't really complain about, but our wins over PSU and IU were nowhere near dominating), it was when Tre was battling illness (strep throat, I think). Take him away, and you miss out on a lot because Evan Boudreaux is just NOT a B1G-caliber 5.
But I think even beyond Williams, the team as a whole started to come together. Nojel Eastern figured out that he can score, and managed to learn to shoot free throws too. Grady Eifert, king of the hustle plays, started contributing on the offensive end. Ryan Cline got out of his shooting slump, and remembered that you're allowed to dribble in the direction of the hoop and 2-pointers are legal shots. And Haarms started to realize that if you're fouling out of games, it doesn't help your team win, so might as well start learning to play defense without hacking people. Eric Hunter off the bench provides a surprisingly good defensive presence when Eastern is out. Aaron Wheeler is still a bit streaky, but his athleticism is unmatched. Sasha is turning into a mix of what Cline used to be (sharpshooter off the bench) and what Dakota became (defensively a lot better than you'd think).
But beyond ALL of that offensively, the improvement in Purdue has been on the defensive end. KenPom currently has Purdue 32nd defensively. 6 weeks ago, I think we were in the 60s or 70s. BartTorvik's site says that Purdue's adjusted defense has improved almost 10 points between game 1 and today. That's especially meaningful because a lot of the teams we played early in the non-con were cupcakes, and now we're in the heart of conference play.
All of this is a credit to Painter's coaching, IMHO. He took a team of good players who were nearly all lacking minutes in previous years and slowly built them into a team that plays some amazing offense and some very solid defense. The team was playing strong offense all year. But the defensive improvement has been the difference between starting 6-5 and being currently 21-7.