Well, I'm not a miui guy, but I have to say there's much features I miss since I made the switch from miui to aosp/pa and now CM11.
The design
I don't mean the style design. Someone may prefer miui style over holo style, I like holo style but there's nothing to argue about, just everyone has their own taste. By design I mean the system is well designed which works better comparing to vanilla android. Let me list some useful features I miss from miui:
Status bar & Notification panel
1. Have notifications and quick switches, and possible to switch between them with a swipe gesture instead of have to reach and tap the tiny button on top right, I miss it;
2. Brightness control slider right inside quick settings panel, which is IMO way more comfortable than just using a button to switch between full, half, low or have to tap a tile again and a new popup shows, the less steps the better right?
3. Ability to disable physical navigation keys so that I don't touch them by accident while I play a game - now I prefer on-screen navigation bar so it doesn't really bugs me, but it would be nice to have this useful toggle in CM.
4. Ability to pull down status bar while running a full screen app - this is never been possible without an floating app before Kitkat.
Camera
Flashlight and camera can be opened at the same time which is IMO way more useful than a flash light when you try to capture something in a really dark environment since it helps focus better.
Better People, Dialer, Messaging for Chinese people
Not much to say here, CM is by design a international rom, which may suit English speaking people better but those stock android apps just doesn't feel comfortable to us, they're hard to use too.
Xiaomi Account
Yes, I really do want to use Google service (which I am using right now on CM11) but for the reason everyone in China knows there's GFW so we can not get a reliable connection to Google, and most of Google's service is blocked (like the entire youtube.com domain, which leads to a bunch of problems) So if I want Google, I have to use a secured proxy everyday (which is I am doing now, I can't even get a stable connection to this forum without a proxy) so it's nice to have manufacture run a service that is reliable to use. If Xiaomi ever release the contact sync for vanilla android, I will use it instead of Google service. And about who gets my data, my government, some oversea NSA guys, I don't care - I'm nobody after all.