Are we talking about doorway pages or landing pages? Each are similar in many respects, but are ethically different and have different purposes.
A doorway page is where you spam the index of search engines to catch visitors using a page of no real value which then redirects the user to a different page. It's ethically wrong, and will result in being penalised by search engines.
Landing pages, on the other hand, are perfectly acceptable. These are pages of real value to both human visitors and search engines. They are pages of content specifically designed for users searching for a particular phrase. Rather than having a visit enter your site on the homepage which is full of content about multiple topics, a landing page will focus on one particular topic which, if the landing page is working well, will be the topic the user was searching for.
The idea of a landing page is to give the best quality content to the user, as fast as possible. And hopefully secure a loyal visitor who will navigate further in to your site.
In short, if we're really talking doorway pages, then stay away. If we're talking landing pages, then go right for it, measure the results, and change the pages accordingly to improve the results.