my experience on driving one and being a passenger.
on interior, personally on the 4gen I love the dash, steering wheel, cluster, and center console set up. im not too fond of the seats... especially in the rear. it makes rear middle passenger look super uncomfortable. unlike the 3gen the middle rear seat still looks comfortable. the rear center floor where the driveshaft is looks too square and not smoothly rounded like the 3gen. but that's my only dislike on the interior.
On Exterior... the styling of all Lexus models are starting to look the same. i mean you can still tell a difference but it doesn't seem to make the GS distinct anymore. looking at all the new models they looks to close. for instance take an ES or LS and picture it with a GS bumper. you would hardly tell the difference looking at the front. the new GS just doesn't feel like a big body anymore... it doesn't have that "VIP" Feeling i guess.
On drive ability it definitely feels more sporty than a 3gen. It feels tighter around corners, feels lighter, makes me feel like i got a heavier foot. the seats hug you pretty well too.
Guys please don't torch me on my opinion LOL. but yeah.