I had one for a week and mine dropped calls all the time, touch screen had alot of unresponsive moments browsing , opening apps or double tapping to turn on, notification light did not work ( well known issue) and my notification sounds stopped working after a day..and the camera is really not all that great, Loved the look, smooth sense UI and the speakers but everything else was just to many problems, switched to S5 and really happy
Are you sure you're in the right forum?!?

Did you buy from a shady retailer, and possibly get a knock-off? You're the first and only person I've heard report dropped calls, the first and only person to report browser unresponsiveness, and notifications issues have only been mentioned by a handful of people most of which have reported they fixed it with setting changes. All of the issues you reported sound like they could be linked with a carriers service. What carrier were you using?
What's the signal strength like, does it do well holding onto bars and not drop lots of calls?
Battery life, the LG G3 was excellent, is the M8 good?
Camera, the LG G3 had a good camera, heard mixed things about the M8. I use it a lot in the house taking pics of my children.
What is the performance like when scrolling around and starting apps, any lag?
Sense, is it good or do you turn it off and use a different launcher?
Should I get a 16GB or 32GB, I know you can add in an SD card for extra storage.
Like MDM I've had nothing but a positive experience with the phone. Its the best phone I've ever had. Every where I've gone with it the signal strength has been strong. Its never dropped a call. I get 2-3 days off a charge depending on how heavily I tax it (and I'm on Verizon where the fools never enabled Extreme Power Saving Mode). If you're with a carrier that didn't yank EPSM (Verizon!

) then you could potentially get quite a bit more out of a charge. I haven't used the camera too extensively, but its seemed perfectly acceptable, and like others have said its works a lot better than most phones when taking pictures in doors. Performance has been completely smooth and fast in everything I've done with it. I've never once encountered any lag. Many people on this board have experimented with other launchers (there are numerous active treads about alternative launchers people are using with the phone), but most people have seemed to stick with Sense, and quite a few seem to have come back to it after trying other launchers. Its very much dependent to what you want to do, or never plan to do with your phone. If you don't find Blinkfeed useful, or never use it then you'll have more reason to experiment with an alternative launcher than someone who uses it constantly. Some carriers will not give you an option between a 16 and 32gb model, but if you have the option (and don't mind any price difference there may be) then I'd recommend the 32gb version. There will always be some apps that will not be able to install/run from the SD card, and you can't always move all of an app over to the SD card. Quite a few apps leave part on the internal area of the phone, and only install/store a small portion on an inserted SD card.
People with a lack of knowledge about the phone, and Android itself for that matter tend to be quick to blame hardware for faults in configuration, apps, and user error. Don't be too quick to follow those people. If you have problems (not that you will) or questions this and a handful of other boards/websites can often provide you with quick and easy answers.