Installed WP8.1 DP as soon as it released and found it wonderful for a while. However, the more I use it, the more problems I find. Some of them are listed below:
1. Phone restarts itself, several times a day, without any apparent reason. I had this problem earlier, but GDR3 corrected it. Now it's back again. (My app list is the same as what it was before 8.1, so none of the apps are causing this)
2. Proximity sensor stops working frequently, and I have to restart the device to make it start working again. As in point 1, I had this problem earlier too, but GDR3 corrected it. Now it's back again.
3. I do some heavy work for like a minute, and then I go back to the start screen to find that the icons on the tiles are missing. It 2-3 seconds for them to appear again (as if they are refreshing).
4. Icons on the app list disappear frequently and take a second or two to reappear.
5. Photo hub is slow now. It always takes a second or two to load my albums (feels like I'm using a website, that takes a moment to download a page - doesn't feel like I'm accessing a local gallery). This was never an issue before WP8.1.
6. Updated XBox music is poor. It keeps on loading my collection endlessly. The experience seems so .. "restless". It feels as if I'm accessing music on the internet and not my locally stored collection. 3rd party apps no more show up in the music app. This music experience is way poorer that what we had on WP8. Video app isn't good either.
7. Phone hangs up a lot.
8. Cortana has suddenly started crashing. It now crashes, every single time, within a few seconds of starting.
9. My phone lies with a blank black screen as I write this. It's unresponsive and only a soft reset will get it to restart. I've already done a soft reset at least 5 times and a hard reset twice, since April 14, 2014.
10. Phone takes forever to restart.
11. Whatsapp works fine when I open it by tapping on the app icon, but it ALWAYS crashes when I open it from a toast notification.
I'm an avid fan of WP, and I know this is only a developer's preview, but what scares me is that it's the "almost final" release of WP8.1. I just hope Microsoft realizes these issues and irons all glitches out, and MS and Nokia bring out the remaining portion of the update soon. But it'll seem to be a long long wait, even longer and more tiring that my initial wait for WP8.1, 'coz for now, I'm stuck with this piece of BS.