Direct remake with MGS2 control system? With exactly the same story, rooms, enemy placements and everything? Exactly how is it terrible when it's exactly the same as MGS, but with a more fluid control system?
You missed out Graphics!

Yes thats part of it. The levels in Metal Gear Solid 1 were not designed to be used with Metal Gear Solid 2's control system. You can often enter a room, go into first person view and tranq every guard in the area before moving on. It completly throws everything off balance.
Have you only done Twin Snakes in very easy mode or something? On all the other modes, they spot your laser on your socom and immediatly take cover, and call for back-up, so you cannot always just aim and shoot, you have to do it tactically, like on the original, except you do it in first person view.