I'm just going to come out and say it - this is a mess. If we were talking about cosmetic stuff like a badly laid out user interface or poor selection of wallpapers then I could overlook the issues, but they aren't. These are bugs relating to core systems such as Wi-Fi, cellular connectivity, Bluetooth, and stability and performance.
These are show-stopping bugs. These are bugs that quite frankly should have been sorted before iOS 8 was released, and definitely should have been pinned down after the first couple of updates.
But they aren't.
Over on Apple's own support forum there's a huge thread related to Wi-Fi issues that dates back to the release of iOS 8. These are serious, show-stopping bugs that have been present in iOS 8 since day one, affecting both users who had existing iOS devices that were working perfectly before the upgrade, and also those who traded in their old, yet functional, devices for upgraded that's now not working right.
There are users with five-month-old iPhone 6 handsets that, for whatever reason, have never worked right. There are stories of people who have had their devices exchanged several times in the hope of getting one that works right.
Others have just given up on Apple.
Now, I'm sure that this isn't a situation that Apple is happy with, but the problem is that Apple doesn't give the impression that it cares. There's not even a "we're working on it" message from Tim Cook or any of the other Cupertino executives. Something to give people hope. Affected users just have to wait for new updates to drop in the hope that it will fix the problem.
And the Wi-Fi issues are just one problem in a tumultuous sea of troubles.
Here are some of the show-stopping bugs still affecting iOS 8 users, along with a few possible temporary fixes:
Some users claim that resetting network settings (Settings > General > Reset > Reset Network Settings) helps (for what it's worth, this worked for me), while others claim that wiping the iPhone or iPad and reloading everything back on from scratch (Settings > General > Reset > Erase All Content and Settings) works.
Some have found that deleting all paired devices works, but the most reliable fix for this is to wipe the device and reload everything from scratch (Settings > General > Reset > Erase All Content and Settings).
No cellular data connection
This seems go away when toggling the connection (Cellular > Cellular Data > Toggle Off) or toggling airplane mode on and off.
There's a lot you can try here.
First you can try deleting and reinstalling the app (this could cause data loss, so take care), and if that doesn't work then you either have to wait for an update or find an alternative app.