In terms of retro Nintendo games (barring the most wellknown ones like Metroid and Mario) probably Balloon Fight, it's simple and the movements is pretty smooth, you're not really limited to the cardinal directions and can even go at a slight cornerways thing.
River City Ransom on the other hand was just...confusing and hard, all i remember was getting past some factory and ending up in some town with a Spa inside, for really old games, reading an FAQ could ruin the journey of it due to learning potentially beneficial bugs instead of uncovering them yourself.
Also, The Moon, which is strange for a soundtrack to hear straight away as one of the potential stages you could start at, instead of some final world music.