This are the cons and the problems I face while using the Htc one M8, That really makes me Hate this phone. This are only my personal reasons and disadvantages,although other user may have different experience. I had a One M8 for a short time but returned it for this reasons:
BlinkFeed and gesture control is annoying:
The UI was crap. Blinkfeed is annoying, and the gesture controls worked with the screen off and locked, so in my pocket i would have my phone unlock straight to Blinkfeed, or activate voice actions, or randomly unlock. i think it's called Motion Gesture but it's very annoying. The Touchscreen is too sensitive and it gets triggered by accident too often.
Remote app slow to Respond:
The remote app took a few presses before my entertainment equipment registered it. aka, three taps of 'on/ off' to turn the TV on, five presses of 'volume up' before it took on the TV.
Design and Hardware failure:
All in all the M8 felt out-dated. The design is two generations behind, it has huge bezels, those speakers really don't feel and worth the hype, and the screen is tiny compared to Samsung galaxy Note 3.
The hardware wasn't well-built. Let put the arguments for metal vs. plastic aside, the Bluetooth in mine stop working after a week. My Android Wear watch just refused to connect to my M8, even after factory resetting both of them. They just refused to pair anymore. I tried a Bluetooth headset and it failed to pair as well. Then I attributed it to hardware failure. this was the main reason i returned the phone. i was still within my 14 days period.
The screen color accuracy was pathetic.The emphasis on green was high, while blue and red were very low. you can see this when you open the Play Store.