I can say that at least for me, AP1 is way better than it was in 2015. Earlier this year, I drove an AP2.5 service loaner for a few days (with EAP) and I thought that its lane-keeping quality was generally on-par with my AP1 car (not dramatically better or worse). This was a pleasant surprise to me, to be honest. I would have been comfortable taking that loaner on a long road trip and driving it the same as my usual car. Also, this was one of the first releases that had Nav on Autopilot, and even though I still had to confirm every lane change, the potential in this system was pretty exciting.
Things you don'l hear much about anymore that were once commonplace for AP1: Exit diving (where AP1 cars used to prefer taking exit lanes rather than staying on the freeway). Truck lust (the tendency of AP1 cars to sometimes scoot closer to semi-trucks that they're passing). Not saying that these never happen, but in general they seem to happen much much much less for both AP1 and AP2/2.5/3.
I'm trying to think of problems nowadays that we didn't have before...phantom braking is one that comes to mind.
I remember when AP2 cars first got autosteering capability. If I could characterize the general opinion at the time, it sucked. It was weavy and speed-limited. What you guys are driving nowadays in the Model 3 is way better than that.
I'd say that when AP1 was actively being worked on, there were various releases that were better in some ways, worse than others. We sometimes had a feeling of regression for some releases. It seems that's what AP2/2.5/3 are going through now. Like there's progress being made, but it's not a perfect process of improvement either. It's difficult to generalize because across the population of Tesla owners, people can have widely differing experiences, and it's difficult to exactly characterize the system's behavior as a whole ("the plural of anecdote is not data").
Bruce.