Metal Gear 1 & 2
First off, let's just clarify that we DON'T mean Metal Gear Solid 1 and 2 (though a proper MGS1 remake that stays true to the original, unlike Twin Snakes, would be nice). We mean the old, old, Metal Gear games for MSX - the ones that your grandfather tells you to shuffle closer and listen to a story about.
Alright, it's not that old, but nevertheless, it's pretty hard to play today.
Also, the plot of Metal Gear 1 & 2 actually ties into the Solid series quite heavily, so for many that have played the MGS series, but not the original MSX games, they're missing out on key parts of the plot.
Granted, you can load up Metal Gear Solid 1 and read a brief plot synopsis of each game from the main menu, and the expanded edition of MGS 3 - Subsistence - features Metal Gear 1 and 2 as bonuses on one of the game's three discs, but we actually want a proper Metal Gear Solid-style remake of these two games.
Full 3D camera control, lengthy cutscenes - everything. We want to infiltrate Outer Heaven, sabotage the TX-55 Metal Gear, take on Metal Gear D, and have a showdown with Gray Fox in the midst of a minefield - all in glorious high definition.
Call it Metal Gear Solid 5 if you wish, Kojima. We'd just like to see it happen.