I bought an S2 around 3 months ago and love it to bits. It's fantastic. Although, it does help if you're already familiar with Android.
A friend of mine, came to the Android platform via iPhone 3GS and found it a difficult transistion. Although, he raves about the S2 now.
My wife has had an iPhone 4S for around a month and having played on that for some time, I'd rather have the S2 - Great all round phone and does everything with ease.