I switched from the M8 to the Turbo the day it was released. I was getting absolutely terrible battery life with my M8, so I figured even if the 2-day battery life claim didn't materialize, I should at least get a full day. And, I have. I get at least a full day with the Turbo, usually a day and a half. I use my phone pretty heavily and when I take it off the charger at 7am I'm usually down to 50-55% by the time I get home from work at 5pm. For comparison, I would often have to charge my M8 at work to make it through the day.
The M8 was my first Android phone, and while Sense is supposedly one of the better manufacturer skins, the near stock Turbo is such a joy to use in comparison. It's noticeably faster than the M8, of course due partially at least to better specs, but it truly is buttery smooth. The screen is fantastic. I did have a slight yellowing of the screen at first, but I think that was just due to it being hot off the presses. It has since subsided.
Anyways, if you're on the fence, I'd say make the leap. The Turbo blows the M8 out of the water. Aside from possibly the Nexus 6, the Turbo is the best Android device on the market right now, and for me, personally, I don't think I could deal with the Nexus 6's larger screen. The 5.2" display of the Turbo is about as large as I can go.
Also, the camera, since you asked, seems quite nice. I don't use it heavily, but its noticeably better than the M8's and has far better resolution when zoomed. Never could get a clear zoomed shot with the M8. The M8 does have far more controls, though, if you care more about things like tweaking exposure and such.