I've moved from my 2yr old+ iphone 4 to a Galaxy S3. I like the Android OS and the S3 itself is fast and fluid to use, so absolutely no complaints with usability. I've also got all my music/videos across from itunes as well so have all the content I wanted and with the SD slot can have all of it on the phone at one time.
The one negative thing that has struck me though is that looking at the S3 face on, with brightness on auto or when dialled up to full the on screen whites just aren't white. I'm comparing the white background in e-mail or when browsing the web and they have more of a grey/off white cast to them when sat beside the old iphone or my nexus 7 tablet.
It's sort of balanced out by photo's having more pop than on the iphone screen (I'm talking ones I've taken with dslr, scaled down and viewed on both handsets) but I do wonder if there's something I can do about the off whites ?
What screen mode have you got selected? (In Display options)