The storyline technically ends with Metal Gear Solid 4.I'm of mixed opinion. I'd like to play it but why is it in a timeframe we've already had games bookending it? Perhaps I just am not enough of a MGS fan to "get it".
So the only place to go is back. But there are games everything from the 60s going forward, so without doing a Boss prequel set in WW2 where she gives birth on the beach at Normandy during the D-Day invasion, this is what we're gettting.
And its going to be totally awesome.