Originally a single-terminal airfield constructed by
Pan American World Airways for their Caribbean/South American routes. MIA later became a hub for
Eastern Airlines and, after
airline deregulation,
Air Florida. When all three went out of business in the 1980's and early 1990's,
American Airlines took over the lion's share of Miami operations and built a major
hub there, which still accounts for most of Miami's passenger traffic today.
Miami is an incredibly dreary airport. There's no lighting and even less spoken English. Plane-watchers may like the view because MIA hosts a variety of airlines that can't be seen anywhere else in the United States (Copa, Lacsa, Aero Continente, Aces, etc.)
The only pleasant parts of MIA are the airline lounges, the new and colorful interior of Concourse A, and the feeling of relief when you get the hell out of any other part of the terminal.
MIA has been under construction for some time. The terminal is a semicircle with concourse piers that radiate outward, and the current plan is to expand a couple of the piers into each other to allow for a few more boarding gates. Of course, the idea is ridiculous, but it's consistent with Miami politics.