Again, games have not gotten too easy..
You just have more freedom in them to make decisions.
In the olden days of yore, the only "moves" you had were the preset moves..
Jump.. move forward.. shoot button.. shield button.. duck..
You moved across a 2D linear landscape where little to nothing changed and in many cases it was the limitation of your character that made the games difficult.
Now you have so much freedom, you can attack a situation based on your own play style.
Still depending on how you PLAY a game, it's difficulty can vary..
For example, Demon Souls, Devil May Cry, and Ninja Gaiden will absolutely PUNISH any gamer who just goes into every situation with a "devil may care" attitude, guns blazing, and screaming incoherent gibberish about the lamentations of women. In those games, assessing a situation and using your environment, skills, and the knowledge of your opponents help you advance and if you are good at that, the game tends to be easier.
On the flip side, games like Halo and Killzone require quick trigger fingers and battle-honed reflexes. Think too much about situation and you'll quickly find your lap filled with grenades. Only the quick and the dead survive in those areas and people who like to spend time carefully considering how to best decimate their opponent often find themselves hitting the "Start Over" button after the "you are dead" screen.
So really, it's about differences in play styles and the abilities of your game character. GTA IV is a prime example... Some missions can be easy or super hard depending upon how you approach them, your prep work, or your reflexes.
Freedom makes games seem easier.