personally, i'm just not a fan of all singing all dancing flash sites.
Principle reason is that they are irrelevant to the content and a hinderence to getting at the content.
The typical example I mean is that you hit the front page of a site. You get a scrolling bar for a 5 to 10 seconds as the animation loads. When the flash starts you get the all singing all dancing intro of moving objects graphics morfing about and looking cool.
Finally find the "Skip Intro" button. I've lost upto 10 seconds just waiting to be able to skip past this bit.
Then you get another 5 to 10 seconds while the main page loads and dances about.
Find the button your looking for, another 10 seconds waiting on the animation. and again, and again.
To me, it just gets in the way and its a constant 'waiting on the animation' rather than getting to the stuff you really want.
Second thing i find that gripes me. Flash sites are often small. The buttons are small, the text is small. the content opens in a small text box which you have to constantly scroll though. There often is not a simple way to scale up the text so you can read it easily.
Dont get me wrong, there are some great sites out there which have flash content, but more often than not, i just find it frustrating.
To me, and i stress this is personal, a good site needs to be:
Relevant
Have a simple method of mavigation
Clean crisp graphics
Quick
Scaleable so that fonts can be enlarged to suit users
http://www.stopdesign.com
is a good example of the type of site I like.
but again, its always personal