Just came off driving a 14-hour combined LA area<->SF area trip this weekend, and I have refined a description of the problem.
It seems to have way, way, way overdone the smoothing on detecting false reactions. If the car is approaching a stopped car, it keeps speeding towards it til the VERY last second it can hammer the (real) brakes to come to a stop. I pretty much always have to brake early to disengage AP and stop, or swirl down the speed setting to get it to start slowing down. It's REALLY bad at higher speeds coming to a stop (e.g. a road with a 45mph limit, going 50 and still getting passed) - as it really just does not seem to notice the cars stopped ahead at a light. (This is with stop-light detection disabled, as I got tired of it braking for every god-blessed sign with a flashing yellow light on it)
On accelerating, it behaves similarly - but the behavior can be different. It seems to have two different modes: one, "throw a chain to their bumper and follow it", and two, "be drunk mode". It'll fall out of "chain to bumper" mode and revert to "be drunk mode" if there's any reason for it to decelerate - and most commonly, that's because of a change in acceleration of the car it's following (e.g. it's a stick shift and they clutch to shift), or if it's crossing an intersection and the car decides it wants more following distance. Then, it'll fall back to "lazily resting its robot foot on the accelerator" and ... make traffic behind me angry as the leading car gets further and further away.
When changing lanes, that's probably the most frustrating part of its problem. If you're trying to get around a very slow-moving car (e.g. 50 on a 65 where traffic wants to go 80 but I keep it to 72), you have to make your move, then immediately track to the speed of the car in front of you. That's how it works - you blend in with the traffic you merged into. But AP doesn't... it'll change lanes, be completely in the new lane, and "la dee dee, slowly accelerating, sucks to be the guy behind me
". Extra large yikes from me. I pretty much always have to goose (to put it politely) the accelerator to remind AP to keep up with the car in front.
When in traffic on the freeway, with heavy traffic it generally performs okay, as it will use a lot of the "chain to bumper" mode (sometimes creeping further into their bumper than I'm comfortable, but almost always
entirely disregarding my following distance setting and being almost too close), but in medium-speed-moving traffic, especially the more dynamic it is, the more I wish I had an acceleration-inhibit (without disengaging) as well as an acceleration-inducer pedal.
In general, the common theme is that its reaction is significantly delayed, and often comes close to causing
its own forward collision warnings. That worries me about how Tesla is planning to use FCWs in FSD Beta eligibility. In this case, I just really wish we could get back the behavior of earlier AP, which was much more robotic and predictable in its acceleration and deceleration, reliably tracking the cars around it.