It's not really "random", there is a coherent story (and a moral to that story) underneath all the weirdness and you'll sometimes forget how crazy it's gotten because your current objective tends to make sense (ex: "defuse the bombs").
But all MGS games are basically playable Kojima manifestos with sci-fi trappings. The actual minute-to-minute gameplay for them is really, really good so even if you don't dig the story they're worth playing.
The previous poster is right that MGS4 does clear a lot of this up. But MGS4 also slams more weirdness and callbacks to the previous games on top of it.
But all MGS games are basically playable Kojima manifestos with sci-fi trappings. The actual minute-to-minute gameplay for them is really, really good so even if you don't dig the story they're worth playing.
The previous poster is right that MGS4 does clear a lot of this up. But MGS4 also slams more weirdness and callbacks to the previous games on top of it.