I like that you are trying to minimize the amount of UI chrome space on the phone and that you're trying to keep all the phone interactions within easy reach of the user's thumb. The notifications tray is just a flick up and the app menu is just a flick from the side, just like Windows 8. I see why you put it on the left, but most people are right-handed, and it should probably be on the right side of the device. I have three problems with it. Well, four if you count any similarity to the Win8 UI, which I am slowly growing to detest. The first is that it gets rid of my favorite UI part of Windows Phone: the always-visible-if-it-exists menu right by my thumb with the action icons. It's a really elegant solution to the whole hamburger button or menu key (on old Android versions) UI disaster. I would miss the icon buttons a lot as a dev. The second is that you now have a persistent status bar all the time on screen. It uses less space for the UI than a menu with icons, about the same as a compact menu and uses more screen space than an app with no menu at all or a pano. Lastly, it's different than the other, more popular, mobile systems. Android and iOS both have the stats bar and notification shade swipeable from the top. Overall I like it, but I would prefer the current menu and I'm not crazy about the colored strip on the side.
I'm not feeling the home screen. The design looks great and I love the look of your 4x4 and 2x4 tiles. I think Files, which aren't that important to the average user, and Search, which is the magnifying glass button on the bottom of the device, don't really need to be on the home screen. I do like that you've made it a pivot rather than the "how do I get to the other programs?" thing WP has now. My mother had her 928 for months and didn't know how to get the rest of her programs until I showed her... The time and weather (no date?) is cool-looking, but it's not doing anything a 4x2 live tile couldn't. (Seriously, make that app.) The time is also on the persistent status bar. This is one of the few live tile designs I've seen for WP that doesn't look completely cluttered. I'm still skeptical about the idea.
Your lockscreen looks fantastic, but it has less info and looks less customizable than the lockscreen on my current phone, which has the time, date, temp, appointments and - ironically - the status bar.
Overall, a really nice design with very innovative ideas about the notification shade and app menus.