So addictive, that it deserved more attention
Enemies are not very varied, and it is not a very big problem. One thing I didn't liked for this game was enemies with guns, and they always run a distance before they shoot (of course, they also run pretty fast).
Also, one very good point is that you can select levels which to play, giving you little less linearity.
Graphics for NES also are very good. There are also cutscenes, and they are pretty well done. Don't afraid of it's obscuriness, it is pretty addictive game.