In Mega Man X, there was a part in the first level that required you to figure out how to jump up the wall to get out of the hole you were in. This was one example of being forced to learn a new skill on order to progress. You're in the middle of a fight, and the floor beneath you drops down and you are forced to figure out how to get out and continue on with the level. In order to get out you must jump repeatedly up the wall in order to get back up to ground level, so that you may continue to play the game and progress.
At first, yes it was a little difficult to observe while I was playing because I was still trying to figure out the game. As I progressed it was easier to notice the game mechanics and the actual design of the game. Some enemies only took a few shots to kill, others took some more. With the game itself, the effect that it was trying to act 3D was rather interesting. The cars the drove in front of you and behind you, but didn't hit you or were untouchable to you.
All the functions that were necessary were all placed on accessible buttons. The arrow keys moved the player left and right, D was jump and W was shoot. The less accessible button (C) paused the game, and is a necessary function, but not for game play. Other then C, there weren't really any unnecessary functions or buttons required for game play that were harder to access.