It depends on many factors. In general the golden age was the decade between 1994 and 2004. Since 2005, quality has been dropping. The main problem is that companies:
a)Have become greedy
b)Don't want to make games anymore, they want to make movies.
We still have Nintendo and the occasional gem like Skyrim and New Vegas, but i have been playing games for more than 25 years on all platforms and i find myself increasingly unable to give a damn about most modern "AAA" releases. If not for my 3DS, i would have probably dropped gaming altogether.