I have the Pioneer head unit. It is the top of the line model. After using it for a while, I ABSOLUTELY HATE IT.
-Using maps at night doesn't go into "night mode", so remains so bright, it blinds you.
-The voice commands are horrible.
-Dictating text messages is a recipe for some hilarious misspellings--so you can't use it in a professional context.
-It loses connectivity sometimes.
-CarPlay occasionally crashes the head unit.
-It can be unresponsive for 30+ seconds.
Much of this is probably an issue with the hardware, but I bet all other cars will have the same issue since Apple isn't making car head units. If they want this to work well, they better make head units. Right now, it is more annoying than helpful.
Funny, but I've got the low-end Pioneer AVH-4000NEX, and LOVE IT - the funny bit is that I've experienced pretty much all the same issues; maybe I just have lower expectations. There is a firmware update that's been out for a while, but I haven't gotten around to installing it - so some of these issues may have already been resolved.
When Siri works, it works great, when it doesn't, it's impossible. The voice recognition is generally really good, it just doesn't get context, and I don't always hit the exact wording to make it click.
The head unit goes into a darker mode when it detects the lights are on (I wired up the appropriate input when I installed it), and I swear at one time the maps screen had a dark night mode, but either that feature went away or broke, because yes, the maps are WAY too bright at night - even with the dimmer screen setting - but I've got it mounted low enough it is tolerable, or I just keep it on the much darker themed 'now playing' screen.
From what testing I've done the text dictation works very well - I just don't use it all that much.
The head unit itself locks up and reboots after 2-3 hours of continuous use - could be heat related, although it's done it during a Minnesota winter, so I think it's something else. It just comes back on its own after a minute or two, so it isn't a huge deal.
I've had the system as a whole run really poorly (once) - the maps only updating every couple minutes while driving, but after it got shut off and on a couple times (as I parked the car and went on to the next destination) it cleared up.
I tied it into an aftermarket backup camera, in a car that doesn't have steering wheel controls or groovy integrated environmental interfaces - I just swapped out the OEM 6-disk changer in my '02 WRX, and it was such a HUGE improvement even with the glitches I'm still giddy about it.
I actually considered getting a '15 WRX, and the lack of CarPlay was a consideration in not going ahead (along with no hatchback option - and the elephant in the room - I didn't have $36k laying around).
Overall, I think it rocks that I get an updated car system with just about every iOS update Apple releases, and can add new apps to my dash. I'm confident most of the bugs will eventually get ironed out, but honestly I'd prefer an infotainment system with 400% functionality and 90% reliability over one with 15% functionality thats 100% reliable. If it had been a $4000 upgrade in a $40k car I'd be pretty pissed; as it is, it gave a new shine to my old beater, and saved me a ton by staving off that 'need a new car' feeling.