Once you reach level 256 in Pacman the game glitches out and you get this:
I've never gotten that far of course. I am not very good at Pac Man.
lol
Also it depends on whether OP is referring to the absolute number of people who completed the game or the percentage of people who played the game that ended up finishing it.
I'm referring to the percentage. If we're talking absolute numbers, games are far more popular now than they used to in the 90's, so modern games will have an advantage here.
Also, I should clarify that I'm talking about full games with proper endings, not mini-games like minesweeper/solitaire.
I'm actually one of those people who tried Oblivion/FO3, wandered aimlessly for a couple hours, then got bored

They're just not my type I guess, though I'm somewhat interested in Skyrim; it looks beautiful judging by the previews. So maybe I'll end up enjoying it, who knows.