So I bought the M8.
First impressions...
1) It's biiiiiig. Substantially bigger than my old One.
2) It feels "cheaper". I mean, I know it's aluminum and all, but it doesn't have the same feel like the original One. It feels empty inside? I think it's too light for its size. The original One felt like supreme premium, perfect size to weight. This one doesn't

3) The volume button is sticking out and happens to be on the way to the power button (which is now on the right) when I'm trying to shut the screen off. I change volume on occasion when trying to shut the screen off
4) Double tap to turn screen on or swipe up to immediately unlock are really cool. It's just that they don't always work for some reason

Maybe once in 50 times it doesn't work and then I have to reach for the power button. And I do it more than 50 times a day, so it's a bit annoying...
5) No opinion on battery life yet, feels a bit better, but I'm already at 60% after 10 hours. Though I must admit I used the phone a lot today, the original One would fare worse.
6) Camera is sick sick sick

That depth thing is sooooo cool and works REALLY good!! I really like the pictures and also others went "wow!" when seeing what it can do

7) Speakers are louder and cleaner - so that's good.
8) I like the onscreen buttons a lot more than the capacitive ones on the original One. They disappear when they're not needed. They always work. You see them when you want to see them. And you always see them when they're there (my capacitive buttons on the original One wouldn't keep backlight on... I never got used to using them in the dark)
9) Speed - it does feel buttery smooth. I have yet to see a single hitch, the original One has its "moments"
Do I like it more than the original One? I don't know yet... I need to get used to the size, as I can't use my pinky finger to keep it secured when holding for example. It does feel more comfortable in my hand (not as sharp) but at the same time it feels fragile... not something I would expect from an all-aluminum phone.