I've tested (during test drives) multiple vehicles with adaptive cruise control, and the 2015 Yukon Denali is the 3rd vehicle I've owned with it. Adaptive cruise control, unless you exclusively drive on a farm or curvy country back roads, is definitely worth it. When my wife and I make a list of features for our vehicles, it is a "must have" with no exception. We both use it daily.
(As a side note, these vehicles, with adaptive cruise to 0 mph, lane departure assist, auto windshield wipers, automatic high beams (which GM missed on these), etc., really are starting to drive themselves. Obviously you can turn these features off when you want in case you forget what it's like to drive.)
In regards to GM's implementation of adaptive cruise control, my wife and I love having adaptive cruise control and wouldn't have it any other way, but we both agree that GMs is by far the worst we've owned. I know there's a lot of other factors to consider for a near 3 ton vehicle, but they just missed the boat on a few things. We're hoping GM can fix with some software updates. Guess only time will tell. Here are the specifics:
- Inconsistent distance. Near, Medium, and Far do not equate to anything we can tell in the logic (i.e., time (ex. 1 sec, 3 sec, 5 sec), distance (ex. 15 feet, 30 feet, 45 feet), or a formula of the either time or distance based on current speed. Whichever vehicle we're driving we typically have it set to the middle setting. Unless in mid to thick traffic, then we (I know this sounds bad) set it to near. If we don't then people (who don't have or understand adaptive cruise) think we're the slow one and pass on the right. It seems like the Yukon Denali just can't get the distance to be consistent. It's seems like when traffic slows, you come up way too fast before the system kicks in. We still haven't gotten used to this and still hover our foot over the brake as we don't quite completely trust it yet. We've never felt like this in our other vehicles, even from day 1. Along the same lines, it's like the system then inserts a delay (like a second or two) when traffic picks back up before it decides to start accelerating again.
- (I have some pretty big heartburn on this one.). When you override the system by manually accelerating over the set cruise speed and then let off the gas, it does a hard brake to get you back to the set speed. This is really annoying. No other manufacturer that I know of does this. They simply let the vehicle "coast" back to the set speed. For instance (using some legal speeds)...You have your cruise set at 55, you come up on a car going 45, you follow for a while until you get to passing zone, then you pass. During the pass you go 65 (assuming it was a two lane road and it's not a long passing zone). As soon as you complete the pass, you're still going 65 so you let off the gas. At this point the Yukon does a hard brake to 55, then starts cruising as normal. If for some reason you ended up going 70 or 75 during the pass, it's noticeable enough that our 2.5 year old asks if something is wrong with the Yukon. We get a chuckle out of it though.
The best system we test drove and ultimately own is on the 2011 Jeep Grand Cherokee. They got it right for keeping a consistent distance, accurate detection (it does have false positives from time to time but that's expected on any of these systems), and intuitive use.
Our 2013 Audi S4 is very good but not as nice as the JGC. There aren't any steering wheel controls (isn't any room due to the S4 smaller steering wheel/style) - instead it's integrated on one of the levers, it doesn't ease (brake and accelerate) as smoothly as the JGC, and when adjusting the speed it does so in increments/decrements of 2.5mph.
We're a tad nit picky, but having an adaptive cruise control system far outweighs not having it.
As for stop & go (i.e., all the way to zero, and then start back up by pressing the gas or pressing resume (depending on manufacturer)), is starting to become more common, especially for those vehicles that already have had an adaptive cruise system. And yes, the current JGC and Dodge Durangos do have stop & go.
I asked because I thought I read somewhere that the system in the new Dodge Durango worked in stop and go traffic and would actually bring the car to a stop. But in addition to being lazy my memory sucks so I could be wrong. 
