On my third day. Too early to tell about battery life, but it has worked for me so far (I am more of a moderate user). I am not impressed with the "quick charge" though. It takes longer to charge than my G4 did. I might try another charger to see if it makes a difference, but the one that came with it is not very quick!
As for brightness, I have it set at 75%, same as I had my G4. Seems plenty bright enough for me, although I haven't had it outside in sunlight yet to see how that looks (it is snowing here in New Hampshire). I love the feel in my hand and the look is great too (I have the black one). No lag and, even though it is an 821 and not an 835, it screams compared to the 808 in my old G4. I have only taken a few pictures, but am happy with what I see so far. I do use the camera on my phones a lot, so hope to get to taking more pictures, and learning all of the features, very soon. Overall, I am happy with it so far.