I have both the M8 and now the 10.
The 10 is much the same as the M8 in the respect it has HTC version of Android, but it is by far the better phone.
Clearer and more vivid screen, good battery life, superb charging time (note the new USB charging port) and much faster OS.
The one thing I’d read was the anodising can scratch easily on the aluminium case, so I bought a spigen case for it from day one.