Mega Man 1 and 2, NES.
Made part 1 my bitch. I last beat it back in the 80s or something. It took a few hours to finish.
Then started on part 2, which I also last beat about 20 years ago. A better game overall, but man, they really toned down the difficulty from part 1 to 2. I got to Dr. Wiley's stage on one credit (whereas it took multiple tries for some of the individual robots for part I), before putting the controller down for the night. I'll kill this one off tomorrow.