I have tried a couple of cases for the S2 and while they have been absolutly fine I wanted the official Samsung case.
It is superb and adds virtually no weight or bulk to the phone. The back of the case is covered with small holes and it looks stunning, although I suspect these are there for a more practical reason, to keep the phone ventilated. There is also a cool Galaxy S2 logo in silver at the back.
Please beware though the case does not offer protection to the top or bottom of the phone. While this does not bother me it may be a problem for some.
In my opinion the case offers lightweight protection and is designed to spare your phone from the odd bump or knock. I would not get this if you want hard core protection.
If like me your are over protective of your gadgets and rarely damage them but want something to give you some light protection and look great this may be for you.