What games have you played so much, that you can beat them in a single sitting? Games you can beat without using a continue, games you've been playing for years, but you keep coming back to play more.
Anywho, here is my list of games I've probably beaten three or four dozen times each.
Donkey Kong Country 3; I can play threw all the level's (other than the secret world) in a single sitting and lose less then five times. (losing 5 times or less is a guess) Just a week or two ago I sat down and played threw all the levels, then went back threw and got all the bonus coins, then the DK coins. It took me three sitting to get all of that.
Super Mario World 2: Yoshi's Island; I can beat this game in one sitting, I've beaten it probably a dozen times, so if I want to beat it in a single sitting it takes most of a day. Thats not geting 100% in all the worlds.
Contra: I beat it for the first time in college about two and a half years ago. It's one of my favorite NES games, whenever I'm bored, or I have to go to work in an hour or something, I pop in Contra because you can play it for a short amount of time and get on with your day. I havent played it in a couple weeks, but I can usually beat it in a single sitting. I usually have to use a continue though.
Crash Bandicoot 2 and 3: I've beaten both probably four or five dozen times each, when I first got my Playstation it took me two months of saving my allounce to buy a new games so I didnt have many games. So I ended up playing Crash 2/3 over and over and over again. Now I can sit down and beat Crash Bandicoot 2, then Crash Bandicoot 3 in a sitting. Now going threw and geting all the gems, and the time trials is a different story.
Boogerman: I was in elementry school when I got Boogerman so I only got a game on my birthday, two or three for Christmas, then usually one or two threw out the year for good behavior, or good report cards or something. So I played the hell out of it.
Bubsy: Same deal was Boogerman
Sonic the Hedgehog 2: Same deal as Boogerman and Bubsy.