If I recall correctly, MGS:R is going to be a Spin-off and comprised of fast-paced gameplay without the traditional stealth gameplay of other MGS games. MGS:R is planned to be the western-aimed game while MGS: Peace Walker being the actual next MGS game with the traditional gameplay and japanese-aimed. To be honest, as a Metal Gear fan, MGS:R excites me the least since it doesn't seem to have much going for it in terms of story continuity nor in the famous stealth gameplay. I'd still buy it, of course.
On a side note, I think it's kinda funny that MGS:R's gameplay is called "Lightning Bolt Action".
Every time I read it I expect Raiden to throw lightning bolts at people.