Why does that make a flat design a bad idea?
IMO, flat design, when skilfully used, can look really good. Of course there is quite a bit of bad flat design out there, just as there is of any other design style.
And don't worry, trends cycle with time, so it stands to reason we'll be seeing some more depth on our screens again some time in the not-too-distant future. (Depth of design, that is, not necessarily depth of content ;-) )
