It's not 4G its still 3G, unless you Kent 4th generation. Display is much better, much better battery life. Thinner, 5meg camera with led flash but other phones have better. 720p video recording and editing. FaceTime with front camera, noise canceling when recording. Faster, a4 chip with 512 mb ram. Louder speakers. I like the new glass back but it will break if you drop it. The 720p video you record only uploads as 320 to YouTube. Problem with antenna is supposable software but the bumper case supposably solves the problem. The video recording is so clear and pics look great. iMovie is real nice. Way faster then my 3GS and the battery is way better. The screen looks really sharp. Stainless steel around the frame make the phone feel solid it feels much better then the other one.
Overall I like this one more then the 3GS, just the new design does it for me but with the new camera quality and front camera everyone is amazed.