All of the classic "NES hard" games of yesteryear would fall into the category of short games that I love. But the thing about those was that for the vast majority of players, their first time finishing the game took a long time. For example, it took me a couple months as a 9 or 10 year old to finish Castlevania 3. But I can pop it into the NES today and plow through it in an hour or two. Most of the good NES games were beatable in under a couple hours. But that initial play through was almost always longer (due to having to start over every time you died, limited continues, etc.).