Upgrade 5.0 sure has bugs! But it seems like each one has different kind too. Mine is the bluetooth headphone set. If use, it cuts the wifi off without fail. However, i am contented to use my wired earphone.
If upgrade, I recommend hard reset (e.g. power button, volume + & home button pressed together). I find my phone still very smooth and not much lag. I also removed my sd card and access everything from internal storage - i think this also helps.
The Note 5 is out and there's no replaceable battery feature, so very unlikely I will buy.
My question is - I have been using Note 3 for 2 years. Should I upgrade to Note 4? I know the screen resolution is better, and camera is better and the S-pen has slightly more features.. Is it worth? haha