Here are some of mine: https://www.youtube.com/user/BlogB13?feature=mhee What do you think?
First, welcome. Second, I love mockups. They're always fun to see.
On Notification Center:
Forget "open app". It's too small and it's redundant. I like your 'touch the icon and it drops down' thing for when you have a lot of notifications. Don't combine that with the old style. If there are few enough to show in a list, show a list. Otherwise only show icons and have them tappable. This would be a setting, of course. Users could still pick the old way.
Additionally, swiping to the side on each list item is confusing. You're hiding information from users entirely, and they'll be confused when they see one notification but the app is badged three, for example. Simply put that in the vertical list, either in the list proper or as a scrollable item within the dropdown if you have icon view up. Just like folders work now; visual differentiation therein.
OH! I've just had an idea myself. Scrollable FOLDERS! It would scroll on the Springboard within the folder background area itself* when the screen is too small to show all the apps in a single folder!
*The bit with Linen behind it:
Swipe down to close? I just don't like that at all. It runs contrariwise to both the method of deletion throughout the rest of the UX and the purpose of "moving item downward" throughout the rest of the UX. People will be confused as heck.
Everyone seems to be trying to shoehorn an Exposé-esque view of open apps into the multitasking arena. I understand why they'd want to do that, but I don't get why it's needed. First, it's more bloat shoved into RAM—the dozens of "saved state" images that would have to be stored, since people never actually close their apps. Second, do you really need to see it? I mean, you know where it was, and if you don't remember you shouldn't have to. The app opens right where you left it; that's sort of the idea. Or maybe I'm misinterpreting.
The only time I can see visual differentiation of apps being necessary is if you have open, say, multiple document creation apps (or any multiple apps with either visually similar UIs or purposes). And if you have open (well, have) multiple document creation apps, I'd ask myself why, but that's me. Can you think of any others?
Anyway, that's my take. I didn't comment on the build quality of your mockups because it's good. Obviously there are places where there would definitely be backgrounds that you've omitted them. I think the biggest thing to work on is visual differentiation and removing clutter from the UI, but the individual elements themselves that you've assembled or created look good!
I think it borrows too much from the newest set of Windows Phone OS', hides UX elements that shouldn't be hidden, and that there isn't anything wrong with the hierarchy and order of information in iOS at present. But that's me. iOS right now goes from left to right (literally): "list of contacts", "individual contact information", "conversation with said contact". From most to least complex.
Having a swipe right (entirely hidden, by the way) for "list of contacts" and a swipe down (too close to some crucial buttons that would eject users from their present UI) for "individual contact information" upsets that order entirely. It goes from a straight line (think family tree), most to least, to an L-shape, middle, least, most (top to bottom). People don't think that way spatially.