Originally, the plot for Rising was for it to take place during the period between MGS2 and MGS4...now it's going to take place after the events of MGS4, specifically, after the fall of the Patriots.
Not true on the last statement.....Metal Gear Acid for one. As for the mechanics...I know that there is some kind of "Blade Mode" where it goes into slow motion and you can just slice and dice an opponent/mech/Ray into little bits.
MGS was not the first in the series. There was Metal Gear and Metal Gear 2: Solid Snake. Also Portable Ops was actually a good game, and was legitimate to the storyline.