First of all I mainly give up on games due to poor gameplay mechanics and awkward user interface (gamepad control-mapping to avatar behaviors), and only occasionally 'mood'. I gave up on GTA IV, Bioshock, Prey, and F.E.A.R. because I didn't like how they made me feel - although, I did hate the whole "Pipemania" mini-game in Bioshock. So, assuming that a game's user-interface can be quickly habituated to (so you don't have to pause and think what button/thumbstick combination do you employ to utilize to yield a desired effect, allowing you to forget that you are manipulating your puppet-avatar somewhat and mentally transfer yourself into their shoes to deal with the circumstances that confront them) and it helps if you are slightly 'overpowered' here (i.e. can aim better than an individual enemy, have more health, etc.) as it will help to compensate for the frustrating fact that you are having to mediate your control with a device not dissimilar to Davros's wheel-chair and then the game can be "balanced" by sending a lot of cannon-fodder in your direction. Halo does this with the grunts, whilst the Elites are more on a par with the Spartan (but they all tend to hold back and let you choose how to engage them), Hunters deserve respect, but only Gold Elites generate real fear. However, good though it is, Goldeneye on the N64 remains the best FPS. Whilst Perfect Dark went a bit silly towards the end, so spoiling the mood it had initially set up that when I discovered that there was nothing much beyond the final alien boss, I decided to stop wasting my time trying to defeat it. The same can be said about Super Mario 64 which would have to be the best game I have ever played and I don't really even like platform games! That said, despite wanting to be able to have completed it, I still am minus one star. If you know the game (and you really should) when you face-off against Bowser you seem to get to the end as you get some very nice animated credits. However, you are actually one star short of maximum points. Going through the final level again, fighting Bowser again (who is much, much, harder to defeat) gives you the last star. Why would you want this? Miyamoto said that the Penguin could be bigger... so that means that you can race the Penguin again on the slope on the snowy level (sorry, I forget its exact title... I'm doing this all from memory). Well, I tried to beat Bowser the second time until I decided it was too hard and I was in danger of falling out of love with the game. Just imagine if films were like this - I suppose "The Empire Strikes Back" has a bit of an 'off' ending. Then there is the plot-line for the TV series 'Lost', which seems to walk the tightrope of mystery over the chasm of audience frustration; I expect if it didn't have some potted dramatic flashbacks and sexy actors with unreasonably nice hair no one would watch it.
Secondly, Goldeneye had skill levels, which didn't just make the game harder, but gave you supplementary objectives - extending playtime.
Thirdly, and most significantly with relevance to this thread's topic, Goldeneye allowed you to tweak the settings of the AI aiming, etc. when you completed the game, so you could make it as hard as you liked. This became like an 'anti-cheat' mechanism. You had to unlock it by completing the game on the hardest setting, but could then make it even harder, but in a way that suited your playing style. Whilst the developer couldn't be expected to 'mix' up all the different recipes of game-dynamics that these sliders offered, the aficionado could. It would be nice to be able to change the dynamics of the weapons in Halo 3 Multiplayer Custom Games, so that people could get back the old Halo pistol (as it stands you can only change the damage of all weapons across the board, not one weapon relative to another; pity).
Fourth and finally, Halo: Combat Evolved's level selector needs to be more widely copied. You could complete the game on Normal and reattempt individual levels on harder or easier settings without having to start a new Campaign. So, if you really got stuck fighting against the Flood (and let's face it "The Library" did go on too long), you could drop down to Easy, then go back to Heroic on a later level. Bungie wouldn't let you get the award of 'crossed-swords on a shield' at the end of the Campaign, but at least you had been allowed to complete the storyline and play the parts of the game you could manage in a challenging mode. After all, developers don't always know where the difficulty 'spikes' in their games - yet, I wouldn't recommend adaptive or dynamic difficulty, which some developers have suggested, which is where a player is analyzed and the game stops killing them repeatedly if they get particularly bogged down in some mission.