I'll play games on hard when the AI is genuinely harder to beat and it makes the experience more fun for better gamers. But in 99% of games, for instance COD4, the only change is how fast and how many guys respawn in certain sections. For instance the end of the sniper level , its not more fun, its more difficult but the guys are stupid and its just boring it doesn't bring anything extra. While other parts of the game are identical to playing on easy, i want the whole level to have AI who are slightly more accurate, move a little more and use tactics and throughout all parts of the level, not 3 choke points having extra guys to make it "harder".
AS for achievement points and the like, couldn't give a hoot, so immensely pointless. Getting more and more fed up with games that lack content and try to persaude you they are good value and long games because you should replay every level over and over and over.
I want more of a challenge in games, but realistic, not normal accuracy guys then on hard mode they are 99.9% accurate and the instant you stick your head out you're dead, needs to be a balance. Going back to COD4, i think on normal or to a lesser degree, hardened, its simply a fun game, but veteran just feels like a chore. As i said 99% of the game is the same anyway, its just 3-4 points in a level they up the numbers and make it a dull luck game rather than challenging. Finding so many games flat out easy, really easy to solve puzzles and map layout, so basic and putting the difficulty up doesn't change anything to make it more interesting.
Can't see how you can play mass effect 7 times though, I played through once, thought it was brilliant, 2nd time, its you know, all but identical despite playing a very different character and taking the more evil route.