The M8 has been out a good long time. the M9 is the current flagship phone that came out early 2015. The M10 is due out in March or April i think.
The main issues the reviewers had with the M9 simply seemed to be that it wasnt too different from the M8 – camera was improved, battery life improved.
I upgraded from the One M7 last Nov to the One M9. Really happy – battery wise, it’ll last a good 24hrs sometimes 48hrs compared to 8-10hrs of the M7.
Got a Dot View case for it, which is brilliant – can answer calls, control the music player etc. without having to switch on the phone.
great having a micro SD card slot again. so have put in the 64Gb card i had from when i had a Sensation XE which housed all my music.