OK , I may do the same thing in simplier games
but in FPSs, it just gets worse, because of some aspects:
You may say you're a good player and you don't do that, but I don't know ONE single FPS player who doesn't do it: Save and Load a LOT! Even I do that a lot when playing FPSs. You reach a new area, you save, you die, or gets lots of damage, you load the last saved game, and now you already know where your enemies are. If you get too much damage again, you load AGAIN, and play the same scene AGAIN until you leave the scene with less damage possible.
And also, FPSs depends a LOT on AI, because they try to "simulate" realistic stuff. When you're playing a "simple" game like, say, Ruff 'n' Tumble or Zool, the variation comes in the way the level design are different, and how different enemies attacks you in different ways. it doesn't matter too much if the enemies always behave the same, as they are supposed to do this anyway (I mean, there aren't much they can do anyway). In an FPS, it just gets silly. You would need a VERY GOOD AI in the enemies to make it bearable. The games we see today, the enemies usually tend to stick with the same tactics, and you'll use the same tactics to kill them. HOW MANY times in an FPS I shot through a door, closed it, and waited 'til the enemies would come at the side of the door, just to shoot them? In Half-Life enemies at least throws you grenades, but even that gets repetitive after some time.
In FPSs, there's usually this scheme: The initial levels have like 3 or 4 different enemies. In a certain level, a new enemy comes, and he's hard as hell to kill. After this, you'll probably get a weapon that makes him easier to kill, and he will begun to appear as an usual enemy. Then he will appear a LOT, together with the other 3 or 4 enemies. In other level, another tough guy appears, and after you beat him, you get a better weapon, and he will begin to appear a lot together with other enemies... you got the idea.
In Zool, or Ruff 'n' Tumble, for example (And Zool isn't even good
), each level has your own set of enemies, and each enemy attacks you in a different way. In Ruff 'n' Tumble, again, each level was a nice surprise, because it would show me a LOT of new enemies, and all cleverly designed.
Ow, come on... even the ghosts in Pac Man or the cars in Rally X need more skill to be evaded than the usual enemy in the usual FPS...