Miui is incredible, a combination of Android and iOS with a very clean and neat user interface, only issue that bothered me at the beginning was the lack of an App Drawer, but i have found a solution for that right away, there's a mod called Extended Settings Menu, you can change a bunch of stuff, like the color of the Status Bar / Clock / Carrier, you can also swap the Battery / Signal position from right to left, center the clock, etc..., very useful, it also add an option to activate the App Drawer :) All you need to do is flash in CWM a small zip and install a apk for controlling the Mod.
And finally, maybe the most important aspect of Miui its the high level of customization and the huge community that creates some amazing themes. You can change almost every aspect of the Rom, from the status bar look to the lockscreen style, no need for 3rd party apps, Miui comes with its own Theme app that can handle .mtz files. You have also the option to browse online for themes straight from the app, an excellent features, you'll never get bored with this Rom
Here are a few great themes for Miui: Suave HD Redone, Zorsha Design, Soda HD and the new SkyDark ICS.
There are a lot of Miui version out there, be careful what you choose, not all of them are translated very good from Chinese, i recommend the Miui-Android v2.1.13 version, available for SGS2 and a few other phones.
There's also Galnet Miui, i heard a lot of good feedback for this also, but i haven't tested it yet, right now i'm using v2.1.13 from Miui-Android Team :)
That's all for now, go and flash your Miui asap, you'll be amazed by the new look of your phone, the real HD experience!
I'll leave you with some inside scoops, enjoy!