Is a flash based website a good idea?

Simple. NOPE.

Really, I would say this was a pretty iffy idea from the beginning. It has become less and less necisary over the years, and has lost browser support. At one point, you could pretty much count on browsers having flash installed, or at least being able to install it if they wanted to.

Today though, almost no mobile devices have support for flash, and even a fair number of desktop-type devices, do not have it installed. This means you are losing a significant share of the market with a flash based site, even if you manage to rank in search engines. And in reality, Flash is a significant issue when it comes to indexing your website for search, so you probably won't even get the traffic in the first place. Some big companies can get away with it, through some combination of HTML fallbacks, search engines trying to handle flash, and plenty of good backlinks - but the odds it works out well for you are low.

Sure you can do some cool things with flash, but in the end, your users probably care more about speed than about crazy intros. Ditch the intro. Give your user the content they care about as quickly as you possibly can.