But! More realism is much harder to deal with for developers.
I'm not saying "realism" in the sense that your character goes to work every day in an office, gets caught in traffic jams, etc. I mean realism in the sense of consistent rules.
This can come up in a lot of different ways. For one, the game AI should have to deal with the same rules as the player. In a "resource gathering" game, this should mean that the AI also has to gather resources to be able to build units and structures. Too often designers cheat on the computer AI by having it collect resources, and having it pump out units, but having those two operations disconnected. This means if you destroy the computer's resource gathering abilities it somehow still manages to pump out units. This inconsistency is really frustrating because it prevents the player from finding clever solutions to the problems.
Another one that annoys me is shooter games where the player can carry a bazooka, a heavy machine gun, a shotgun, a minigun, a missile and a few handguns, yet still manage to run. When there's no tradeoff to getting a weapon, it means everyone tends to rush to acquire as many weapons as possible. When people are forced to carry only one weapon, it makes things much more interesting, as well as realistic.
Savegames are the other huge thing that makes games unrealistic. They allow players to do something risky and dumb, knowing that if it fails they can just reload. This is bad. What makes it worse is when designers take this into account and rely on this ability. This allows them to force players to try something risky or overly difficult, knowing they can reload if things go badly. Sure, there's some pleasure in completing something challenging, but what about when it is too hard? I've played too many games where something is not fun because it's too hard, and you just need to be able to get by that one part so you can play the rest of the game.
I, for one, would love to play a game where you had no control over saves and reloads, so long as it was done right. In this ideal game, the only "reload" would be when you started the game up again. It would also be one where you could quit at any point, and when you started up again you'd contine near where you left off. Unfortunately, to do this right you'd have to make sure the game was good. I've played bad games like this that ended up having me turning off the computer instead of quitting the game just so it wouldn't save things. The main difficulty with doing things this way would be to avoid any situation where there would be a motivation to go back. This would mean getting rid of any bad outcome. If it was a sports game, losing an important match wouldn't make you want to do it again. If it was a shooter game, you wouldn't die and have to do something over again.
The best way to avoid making people want to reload when something "bad" happens is to have it trigger something good. For example, in a sports game, if your franchise loses a big game, somehow it makes a superstar player become available. If it's a shooter type game, getting "killed" might have you continue the game on a different, secret level. In a RTS type game, failing the mission on one level might open up an alternative way to win the whole game.
How's this as an example of a good way of dealing with a player failing a few missions in a RTS type game. Because the player has failed a few missions, the opposing computer player is much stronger. However, as a result, the top general of the computer team tries to overthrow 'el presidente'. He fails, but lives, and the computer's army is split in two. All of a sudden, instead of one enemy, you now have two, but they're each fighting eachother. Now, the odds are no longer stacked against you, and you don't have to reload the game. Conversely, if you win every game, the same kind of thing could happen to you -- one of your generals could attempt to kill you, and instead of being in a dominant position, you'd have a new enemy to fight.
Needless to say, this sort of thing would add vastly to the replayability of games. The first time through, you'd lose a lot of missions and see one plot line. The second time through, you'd win more, but still lose some, and a different plot would result. The third time you'd have honed your skills and see yet another plot.
Goldeneye was a good game, but they could have taken some cues from Bond movies. Although he's a great spy, sometimes Bond does get caught. But is that the end of the movie? Does he "reload" and try again? No, he's normally trapped in a difficult-to-escape situation (like a laser slowly creeping towards his crotch) and he has to escape. Wouldn't the game be cool if whenever you "died", instead you were captured and had to escape from some nefarious slow death?
Maybe I'm asking a bit much, but I'd sure like to play a game like that.