HTC One M8 received Android 5.0 Lollipop update last month, but without the Sense 7 UI, which debuted with the HTC One M9. However, according to a tweet from Mo Versi, VP of Product Management at HTC, the One M8 will receive Sense 7 UI with the next software update.
@MohammadAsad528 no, this won't but our next update will include it. Thanks.
— Mo Versi (@moversi) April 7, 2015
HTC Sense 7 comes with improvements to BlinkFeed news reading interface, an extensive theming tool, new multitasking UI with pinch-to-zoom controls, option to add pull down notifications tab in the navigation bar, and slight changes to icons.