Thanks for this write-up!
I'm actually considering trading in my Samsung GS3 for the Optimus G... I know, call me crazy
I am just kind of turned off with the hardware/build quality of the GS3. I played with the Optimus G and it look and feels A LOT more premium.
As far as UI goes, I'd just be using Nova Prime Launcher anyway... so no big deal. Auto brightness isn't a concern with me.
I wish it came in white! I bet it will come out later though.. kinda like how they did in Korea with multiple colors.
My real concerns are its lack of exposure... especially when compared to the GS3. No phone cases, accessories, and possible a lack of software support. Also, I think the GS3 will have better resell value in 2013 than the Optimus G, which says a lot about its prominence in the market. I say that because I'll probably be trading in sometime in 2013 for the next newest and brightest phone.
I'm really on the fence with this because I do love the GS3, it does everything I'd want in a phone... but I did play with the Optimus G and loved how it felt and it was VERY quick/snappy/impressive. I have time though, so no real rush.