Bill writes about both Return to Dark Castle and Zelda today.
There were a few NES games which consumed much of the time I should have been playing outside in my youth. Number one on that list was certainly the original Zelda. As Bill notes, Zelda is interesting historically mostly because of the influence it had on later games, not because of stellar game design. The stilted english translations and inherent limitations of the cartridge format made the game tough to play unless you had access to a walkthrough, which Nintendo Power did a good job of providing every month.
But the amount of time I spent playing Zelda was nothing compared to how much time I wasted playing Dark Castle. I remember it came on two 400k floppies, DC and DC Data, and it took me a while to start it up on the ol' 128 (upgraded to 512k, but no 'e'). Like many early side-scrolling platformers, every time you started the game you had to play from the beginning. I got pretty good at it; I could get the shield 100% of the time, fireball a lot of the time. I could usually make it through Dark Knight 1, and often the game was over in Dark Knight 2. I still remember the first time I beat it, and finally toppled the Dark Knight.
Dark Castle was one of those games that I wished had a level editor. Another game I played a lot around the same time was Pinball Construction Set, and I spent quite a lot of time imagining the levels I would design had a level editor been available for Dark Castle. I remember vividly one time when I sat in the waiting room at the dentist, drawing a Dark Castle level which was a combination of the slide into Trouble 3 and the swinging ropes in Trouble 2.
When Beyond Dark Castle came out, unfortunately the ol' machine wasn't powerful enough to play it. Once or twice a year we would go visit family friends in Lansing who had both an SE/30 and a Mac II (color!). It was the best thing in the world to be able to play Beyond Dark Castle on that SE/30. I never did get enough time to finish it, though.