The saying that 'simplicity is beauty' also applies in websites. Google is the great example of being successful just being simple. From a technical point of view, the more simple your website is, the more faster it loads for your viewers.
A flash website is nice but you would need an ultra fast connection just to view these site as ease. This becomes a disadvantage if you are also targeting area with much slower connection.
More about simplicity in websites, on the link provided below.
