coming from a 3G. after 2+ weeks with an iphone 4, this is what i think:
likes
screen resolution.
speed.
the camera.
battery life seems very good.
iOS4 is good, and runs very well.
dislikes
screen doesn't like daylight. hard to find a setting that works in both low and
bright lighting.
the shape. the old one looked nicer, felt nicer, and was lighter.
the cost
i can reproduce the antenna problem if i try hard to cup the phone with my hands. never had a problem in normal use. i ordered mine with the apple "bumper", as i like to have a case, and that was the only one available at the time.
i
might have experienced the proximity sensor issue once. not sure.
i think the performance upgrade will become more important as apps get developed with the iphone4 in mind.
i'm happy as i came from a 3G, and that's a big step up in performance. might be different if i'd upgraded from a 3GS
shame the only 3GS available, new, now, is the measly 8GB model. no use to me and still huge bucks.