Sadly it is now impossible to do a review of the iPhone 4 (iP4) without mentioning the antenna and the reported issues when you hold the iP4 -- which is a shame because there is so much more to the iP4 than the antenna.
That is not to make light of the potential issue -- I just want to point out there is much, much more to the iP4. To start, there is the Retina Display, which is "clearly" the best screen on any smartphone, period. Then there is the improved 5 MP camera with a flash on the back, and the new front-facing camera. There is the Facetime app, there is a faster processor, double the RAM of the 3GS and better battery life.