"Why Legal Immigration to the US Is Nearly Impossible" details all the US immigration rules, types/visas and the insane amount of process, paperwork and time required to get through any of them. Filled with insightful graphs and hundreds of references. This is a link that must be bookmarked for future reference to consult on the minutiae of US immigration, jargon or stats.
https://www.cato.org/policy-analysis/why-legal-immigration-nearly-impossible