HTC M8 will be announced on 25th March 2014. But everything has been leaked before the official announcement. Now, we have a leaked HD review video of the device showing the HTC One and the HTC M8 side by side.
The above videos shows the full physical appearance of the handset as well as some UI. This is not a professional review so don't expect to see everything about the device but the video gives a great idea about how HTC M8 will be.
The original video has been removed from YouTube as HTC warned the maker for showing the handset. But before that the video was already mirrored so enjoy watching it.