I just installed a leaked Samsung Jelly Bean firmware for Samsung Galaxy S2. It is having some features from Samsung Galaxy S II. You can see few Screenshots below. Am a fan of “Swipe to call” and “Swipe to message” feature of Touchwiz, this ROM have that feature as it is from Samsung.
Blocking Mode, Seems to be a cool feature.
Smart stay helps you to keep the screen on as much time as you are looking on it
Here is the motion settings, Direct call allows you to make call to the contact currently displayed on the screen by just put the phone on the ear.
Share using Group Cast
New File Manage
Two Home screen Modes
Jelly Bean
Lock Screen with Shortcuts
TouchWiz home screen
It includes Samsung Chat On, which helps you to chat and share files with friends who have a Samsung device. Read more here
Android Jelly Bean 4.1.2 for Samsung Galaxy S II (I9100)
You can get free 50GB Dropbox Account too 
Watch a video
Remember to install this ROM you need a rooted device and rooting of your phone can void your warranty, and may brick your phone. So install at your own risk.
You can read more and get a rooted ROM (with brick free Kernal) here