I had a couple of hours to spare on a Sunday afternoon, so I fit in a quick walk down 11th Avenue (called West End Avenue north of 59th St.).
11th Avenue is one of the shorter avenues, running just under 5 miles from 108th Street to 22nd Street. North of Lincoln Square (66th Street) the avenue is almost completely lined by tall (~15 floor) pre-war apartment and condo buildings, most of which would have the word "luxury" in their marketing materials. Below Lincoln Square 11th Avenue runs through the less densely populated western section of Hell's Kitchen, where many of Manhattan's auto dealerships are located (along with the stables where the Central Park carriage horses go at at night). Things start to get pretty gross around 34th St., where the avenue crosses over the massive train yards of Penn Station (located to the east). This is changing though - a massive 27 acre / $20 billion development project known as Hudson Yards is underway to build what will essentially amount to a new neighborhood over the train yards. When complete, Hudson Yards will be home to 16 new skyscrapers and nearly 13 million square feet of new office, residential and retail space. It would get nicer as you move south into Chelsea, but 11th Avenue dead ends into the West Side Highway at 22nd Street.