Houston IMO easily has the most impressive skyscraper canyon feel of the Big 4 in the South(HOU, DAL, MIA, ATL), yet it probably has the least vibrant core of the four. It also has the least transit access. The most developed downtown, yet has the least big city amenities. It's an irony to say the least.
Atlanta's downtown is probably the least big city feel of the four(doesn't have many skyscraper canyons) because development spreaded out between Downtown, Midtown, and Buckhead. But Midtown Atlanta is an impressive beast on it's own which makes the core of Atlanta(DT/MT) feel large. Here's a recent picture of Midtown from the east.
Here's a photo from the southwest:
Midtown/Buckhead both developed along the MARTA rail line which I suppose is a good thing if the development wasn't going to concentrate in the downtown area.