There are some annoyances with Win 10 I've found, and I only do clean installs for my systems.
Privacy stuff turned on by default - nothing really new here, everybody is collecting that data, whether you like it or not. Quick and easy to turn it off if you don't like it
Forced updates - for those of us that are smart enough to look at updates, that's annoying, but can be disabled/deferred. for average people, it's a good thing
App Functionality - if your app was built for Win 7, shouldn't be an issue for Win 10. If your app was built for Win 95, then you might have issues.
Live Tiles - easy to close those and make it look pretty close to a normal start menu
Xbox One Integrate - don't have an xbox so I can care less
Wireless Pass Sharing - Don't care for this, and disabled it immediately. Just because we're friends on social media, doesn't mean I want you to have access to my wireless pass

Switching App Prompts is highly annoying. Click on a link from a PDF, a Tor link from browser and it asks "Are you sure you want to switch applications" all the time...haven't found a way for it to ignore certain ones or disable it completely. Good for average people, but annoying for me.
Edge browser - Biggest pain in the kester so far. Seems to crash after being open for 3+ hours, close and restart it's fine. Links don't always respond like they should, probably just needing sites to be revamped for new technology *shrug* Works fine in IE, Chrome and FireFox; IE still installed and easy to get back to. Internet Options is VERY slim now, and doesn't seem to be functional 100%.
Overall, I like the look/feel of Win 10 over Win 8.1, and I'm sure it'll get better as we learn little tricks about it.