The Galaxy S2 is, quite simply, as advertised, the most powerful smartphone in the world today. Powered by a dual core processor, it however beats other phones who use the same kind of processor (HTC Sensation, LG Optimus) by miles. An application called Quadrant, available for free from the Anroid app store, is considered to be one of the most reliable measures of performance, and measures this phones performance way over its peers.
The Android Gingerbreads performance has also been acclaimed to be much ahead of symbian / windows comtemporaries and leaves noting to desire. I can go on and on about the various features and capabilities of the phone; but as I mentioned above, it is the most powerful smartphone available in the world.
The sound level could be better. However, seeing that such phones are only bought by phoneatics and geeks, they should have no problem downloading software (again from the android app store) which increases the base volume.
The worst part of the phone is that is hangs up, although infrequently. It happened fairly often (once in 2-3 days) when I initially bought the phone, but since I downloaded a firmware updrade, the phone has hardly been giving any problems in that area.
The phone serves a wide gammut of requirements - fulfils the business (emails / spreadsheets / word / ppts) as well as is fulfills the media / entertainment aspects. Has a huge 16bg internal memory, extendable by mmc. The AMOLED display is simply mindblowing, leaves the iphone / itouch / ipod gasping for breath.
The weight is perhaps TOO light, makes you a little uncomfortable as you keep checking whether the phone is still on you. Makes the phone feel a bit delicate as well, although have not experienced a fall.
The price is a bit on the higher side, priced at approx. 30K. Although this puts it on par with the iphone 4, the latter is no match for this monster performer. The iphone 5 is rumoured to fight out this one on performance, however.
In short, the best phone I have come across, without a doubt. Surprisingly a Samsung.