Owning the phone for a few weeks now, i must say i have not been disappointed. I have owned many smartphones including 3GS and i must say i am very impressed with the S2.
Having a duel core processor, a super amoled screen and a large ram, it will load any application in a split second and hardly ever lag.
It has many cool features such as a notifications bar like on the OS5, a widget that lets you link your facebook twitter and other social networks together and display them in one feed. You can also reply from the widget to the social networks. A very nice camera with lots of features. The best feature in my opinion switching from an apple OS is being able to expand the widget to see live information from it without having to click it! Perfect.
There are some drawbacks, it doesn't support .avi playback, you cant switch off 3G manually, the video recording doesn't have stabilisation and there is no notification light.