I'm from Toronto and I travel frequently to London as a tourist. My biggest impressions (not things I love or hate, just differences compared to home that a tourist from my neck of the woods might note):
1. Humidity! Hot or cold, I can feel and smell the dampness before the plane descends. My hair gets frizzy in London and sometimes my skin feels clammy even in chilly weather. It takes a few days to adjust.
2. The tube goes *deep* underground. At some stations the stairs leading down to the trains seem to go on forever; at all stations the escalators are very steep and move very fast. The stations are generally very clean and free of litter- same for the cars themselves- big difference from home. Sometimes there are what I assume to be TfL employees standing on the platform, overseeing what's going on.
3. Architecture is a hodge-podge of styles and eras, very little cohesion outside of certain individual neighbourhoods. From my impression of the areas I've been too, 19th and 20th century architecture dominates. London looks interesting as opposed to beautiful (vs. other European capitals), some of the modern architecture is fascinating.
4. Fluorescent jackets (greenish yellow) on police officers and all manner of outdoor workers- garbage crews, construction workers, those TfL employees who stand on the tube platforms.
5. More visible security- more cctv cameras, more signs warning of the presence of cctv, more signs bearing instructions regarding safety and security. More barbed wire, iron bars, anti-climb paint, and alarms. More police officers on the streets.
6. More "fresh" litter on the sidewalks left by pedestrians. Less public garbage & recycling receptacles.
7. Men dress better, have better haircuts, wear slimmer fitting clothing, don't wear baseball caps. Women dress a little differently too, but the biggest difference is the men imo.
8. Prices include tax, and often aren't rounded down, for example something will cost £2 not $1.99.
9. More scooters (ie vespas) and motorbikes. Narrower streets and sidewalks. Denser concentration of people.
10. High energy, even rushed. People walk quickly (tourists excepted, of course).
I agree with the suggestions of using Google Earth for a look-see. Also youtube often yields interesting results- in general there are lots of "street scene" videos for cities all around the world.