Seriously, I'd suggest he plays the previous games first because there are so many new controls and gameplay tweaks in MGS4 that he might find the gameplay elements in the first games a bit, let's say, underwhelming (no first-person view in the original version of Metal Gear Solid for example, no "weapons shop" and all, etc.).
Random game thought :
Why is Bionic Commando Rearmed 2 getting so much hate? We finally get a real game and they're not even satisfied... I'm starting to hate the gaming community so f****** much...