The food is definitely better both at the higher end and in terms of being able to get decent food at a reasonable price especially as there is such a wide variety of great ethnic restaurants (Indian, Vietnamese, all sorts of South American, Spanish, Italian, North African etc etc). Although that doesn't mean there is still not a contingent of overpriced, poor quality food offerings just that it is a lot easier to find better options! Actually, in terms of becoming "more American" one of the big food trends right now in London is "American" food - lots of new hot dog places, all sorts of burgers from sliders to gourmet burgers, much more barbecue.
One noticeable change is all the new buildings - lots of big new tall buildings going up changing the skyline a bit with the "Gherkin", the Shard, the "Cheesegrater", the "Mobile Phone"... but there's still that great mix of the ultramodern right amongst the terribly historic.