“Doorway pages” are often confused with “Landing pages“, and while they may seem similar, they are quite different beasts. If landing pages are white hat SEO, then doorway pages are definitely black hat. Here’s why:
Doorway pages are designed primarily for search engines, not for human beings. They are often used to spam Google’s index in order to promote specific keywords or phrases artificially. Doorway pages usually only contain thin content are not good for visitors, and very often there is no clear path to conversion or continuation. Google recently introduced (circa mid 2015) an algorithm change designed to identify and penalises doorway pages. That should be a good enough reason to not even consider using such a tactic by itself!
Landing pages, on the other hand, are often used to provide a “first page” experience based around a service, product offering, or promotion that you are running a campaign for. The landing page serves as a destination before online conversion. It is critical to deliver on the promise – the “scent” – of the advert or campaign that sends people there. Once on the landing page, people should then be able continue to explore other parts of the site.