Google's search engine was not the first one ever, and it did not work much different from other search engines from the user's point of view.

So why did it become such a huge success? Because it was better!

With other search engines, you could easily be fooled to enter porn or scam websites, or miss out on the really useful website because of too much attention to e.g. meta keywords that could be manipulated with by "evil" webmasters.

Google introduced not a new concept (search engine) but a new way of ranking search results.

With other search engines, your search interface was cluttered with ads, trying to get your attention away from what you wanted to do; search for information.

Google's philosophy seemed to be along the lines of "let's get hold of the users and THEN we can look at how to make money"

Gmail was not the first free mail service. Hotmail and Yahoo! Mail had been around for ages.

So why did it become such a huge success? Because it was better!

Hotmail and Yahoo! Mail always try to divert my attention with flash banner ads and "important messages" from the staff. Gmail does not.

With Gmail, Google also elaborated on the "new" technology, AJAX, a technology that has been around for some time, but did not really catch on before Google showed the world, how a web page could be more or less like a desktop application.

Once again, Google took an already conceived idea and turned it into their own, with added benefits, better usability and more value to the users.