Flash has long been used to make websites beautiful. The slick, stunning graphics it offers make it irresistible to designers, and of course it is the medium of choice for gaming sites, but with HTML technology catching up, the options for presenting images and content on websites have increased.
The advantages of Flash
Independent of operating and browser systems, Flash websites can be viewed by anyone who has the plugin for that particular program. It's versatile, allows the display of both animated and video content and makes images look slick and smooth. Flash can be added to a HTML-based website as an SWF file or an embedded item such as a YouTube video, and is particularly popular on gaming and interactive fantasy websites.
The disadvantages of Flash
First of all, you need to have the plugin for that particular program, and there are lots of them. So if you're viewing a Flash-based site and you don't have the plugin, you'll either see nothing or you'll have to download the plugin.
Webmasters may find that people don't like having to download plugins just to view a site: they'll move on.
Flash is notoriously slow to load. Since you typically have between four and eight seconds to impress a viewer, this is a major drawback. SEO suffers because Flash- only sites aren't searchable because there's nothing for the search engines to pick up on, i.e. text, meta tags, etc.
The advent of HTML 5 is being touted as the death knell for Flash because it offers many of the features that Flash has, namely the ability to play audio and video content. In April 2010 Steve Jobs of Apple wrote, "... with the development of HTML5, Adobe Flash is no longer necessary to watch video or consume any kind of web content."
Google Chrome, Safari and Firefox already support certain elements of HTML 5 and are tipped to incorporate it more fully into their browsers, eliminating the necessity of downloading plugins to view audio or video content. In fact, Ian Hickson of Google, Inc., is the editor of HTML5 in association with W3C.
The disadvantages of HTML5
Although it has been well-known among developers for years and is a major project in W3C, Flash will remain in use for years to come because issues of copyright are not addressed by a system that just plays audio/video content. Flash enables the companies that produce proprietary content to address licensing and permission issues. HTML5 doesn't.
The development of HTML5 has been slowed by the need to standardize and take into account the large numbers of people who still use older versions of Netscape and IE. Since Flash works well and is widely used, many people and business owners see no need to replace their current systems in the light of the likely cost and steep learning curve.