Hideo Kojima says Physint's happening because you lot just wouldn't stop asking for 'a new Metal Gear' and, after a brush with death, he's decided that's not a bad idea
Personally, I think the pacing for Metal Gear Solids 1-3 are great.
Even MGS4 was solid up until you kill the first boss. (I assume this has to do with Kojima rewriting the rest of MGS4 to appease those sending him death threats for wanting to kill of Snake.)