My son got Coffee all over my 5s, so i bought an unlocked m8. I have been using it for the weekend.
Here are my observations comparing the two.
Some of my own thoughts on top of yours. just opinions of course.
M8:
-Camera is Terrible ( disagree. not as good as many camera phones out there, especially with a light source in the shot, but you can take some really good photos with it imho)
-Battery life is decent(Not amazing, but decent) ( I would say it is on par with the iPhone 5 I had before it which I think is rather impressive, by my last android phone was a galaxy nexus and compared to that this battery is astonishing.)
-OS is smoother than GS5 (don't have extensive experience with the s5 so I can't comment here)
-No bloat on my unlocked version is amazing (I'll bet!)
-Apps arent as good as iOS counterparts (I personally don't know about this. android apps have gotten pretty much on par with iOS counterparts at this point, at least as far as the popular ones are concerned.)
-Google Hangout is inherently flawed compared to iMessage (some would argue iMessage is rather flawed too in some aspects but yes I know what you are talking about with hangouts. )
-Double tapping the screen to wake up is amazingly handy (I use this all the time. easily my favorite feature on this phone)
-Reaching for the power button to turn off the screen is kind of a chore (there's an app for that

I don't remember what it's called but it's a couple tap to turn the screen off. of course it would be nice if that was baked into the OS but.... )
-Speakers on the front are amazing and are a joy to use (AGREE 100 Percent. amazing speakers.)
Sent from my HTC One (m8) using Tapatalk