Most people do not react favorably to the Flash technology. Most of them hit the back button as soon as they find Flash on a web page.

There are a number of reasons for this such as:

Flash is a Plugin
Flash is available as a Plugin that needs to be installed, it doesn't come in integration with the browser. Due to this, whenever someone tries to view a Flash content, they are prompted to install the Plugin. This is a time-consuming process, and the Flash Plugin is not available for all browsers. Every time a flash content appears, it has to be loaded. This wastes a lot of valuable time.

Flash is Slow to Load
After the Plugin has been loaded, the particular Flash movie that you want to see has to be loaded. Generally, these movies are very heavy and a lot of time is spent while they are being loaded. This is generally not appreciated by the visitors.

Flash Makes Sound
Many users have sounds disabled in their computers. However, being a Plugin, Flash doesn't follow these settings. This annoys the users because they have to turn off their speakers to avoid any unexpected sound to be forced on them.

Flash is Often Unnecessary
Some websites use Flash for even minor animations. This is quite unnecessary and is not at all interactive. A good example is the Flash intros that are present in a number of sites. A user has to helplessly wait without being able to do anything about it. This is another annoying feature of Flash.

Flash Breaks URLs
Any navigation made within a Flash movie is not saved at all. If a user refreshes the page or visits another one and comes back, they have to begin from the very beginning. This also becomes very irritating in case the user would have found some information or picture of their interest.

Flash Breaks Right-Click
Right-click is commonly used by a lot of people, to print, save or copy some data. However, right-click on a Flash object displays options related to Flash only. The users are not interested in these options. This option is specially important for the users who like to open links in new windows by right-clicking the link and selecting 'Open in New Window' option.

Search Engines Can't Read Flash
The most important argument against Flash is that it is totally invisible to search engines. Text written with the use of Flash doesn't exist for the search engines. Therefore, it cannot be found by the visitors who might be looking for it.