I’m writing this on an iPhone 4s. Still works as good as the day I bought it about four years ago. I upgraded to IOS 8.3 easily and it works perfectly. Outstanding product HW and SW quality.
My first non-Blackberry smartphone was an iPhone 3GS. I loved that phone, right up until the iPhone 4s came out. At that point, Apple released an OS update. I installed this on my 3GS, and immediately started having issues - 1 or 2 crashes per day. 20-30 second launch times for the built-in mail and some other apps. Even starting a call took 4 or 5 seconds. It was completely unusable - so bad that I was forced to look for an alternative. Had Apple not done that, I would almost certainly have purchased an iPhone 4. But I resented being forced to upgrade, so I went with another vendor.
They've done the same thing again, although to a lesser degree, with my iPad Air. Here's a video that shows my iPad Air displaying the Drudge Report web page. Note the extremely slow rendering of the page as I scroll through it. This gets worse over time, and won't improve until I restart Safari (and then it just goes back to the speed shown in the video - abysmal). Drudge is a very simple web site, with few images and minimal ads, so I don't understand this. My phone actually renders it much better than my iPad. Some websites will also trigger Safari to reset the page and display some message along the lines of "There was a problem with this web page so it was reloaded". This happens *a lot*. Again, I'd be right there upgrading to the latest iPad, but this experience has so soured me that when it's time to upgrade, I'll most likely just get an Android tablet, or maybe a Surface Pro 4 if that's out. Video
But I don't mean for this to turn into a rant against Apple, because aside from these complaints, I do like their products. Like I said above, they make great hardware, and I've had no issues with the non-mobile platform (ie OS-X).