I think, in part, I regret upgrading any of my Apple devices to the 27 line of operating systems. While my experience as a whole has been pretty favourable, the one thing I was looking forward to is not just disappointing, but is a huge step backwards.

I don't use Siri for many things, but I do use it a lot for a small number of core things. On any given day I'll lift my watch up and speak to it to set a timer or a reminder. Occasionally I'll ask other things, but they're the main uses. Thanks to the fairly recent addition of on-device voice handling, these requests have been near-instant.
With the new Siri that comes with iOS 27, etc., if I'm really lucky the reply will be super slow (getting on for 20 seconds or so to do the job), but more often than not it just doesn't work at all. Either it tells me that my main device isn't available right now1 (which I take to mean my iPhone, which is wild given it's always in my pocket at the time), or it just busy spins for ages and then simply times out and does nothing.
If I try to use Siri on the iPhone itself, it either just busy waits for ages without getting anything done, or it finally tells me it isn't working.

I was one of the people who upgraded to the 16 Pro because of the promise of "Apple Intelligence". I was, unsurprisingly, kind of annoyed that they didn't deliver. But it was fine, the phone is a good one and it's still serving me well. Also, if I'm honest, I was comfortable with the idea that they chose to not really implement anything2 rather than implement something bad.
Sadly though, based on my experience so far, they've implemented something bad. Since upgrading, on the Watch and iPhone, I've found that it's either horrifically slow or it just doesn't work. On top of that, I've lost all the benefit of the on-device voice handling of my watches.
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