That mode is basically a hardcore mode.
It changes the story and gameplay to suit Snake. There is no voice acting and soliton radar. It was added because of the backdraft raiden caused.
Wait, the so-called "Snake Tales?" Huh... I thought there was supposed to be a playable segment in the normal release, though.
So, I have to say that it was obvious part of the point was that the "real game" was happening elsewhere. The game where you play as Solid Snake and help the dumb rookie, and get to do all sorts of cool stuff, and where you aren't so likely to slip in seagull shit or pound yourself into the stairs "rolling" (cartwheeling).
And where you can actually hold a person up with a gun well.
All the same, there was a real story to be told, even though you weren't the focus of the mission's story, and were never going to be. And... I don't know. What can I say? I was very impressed.
Even though I thought Emma should have died by accidental sniping, rather than Vamp.
And, more than that, I actually found fighting as him really fun, by the end. Really, really fun. And, surprisingly, even though the difference between playing him and Snake was pretty superficial, I found myself using a really different style...
Yeah, it was great.