Worth the $5, just don't expect a masterpiece
High points: The gameplay is fun, and the levels are often quite different from one another, as are enemies (in movement patterns, health, and appearance). Fortress levels (Boss levels) bring a degree of exploration to the game. Entertaining 'tests' from Zeus give you more power. Enjoyable premise.
Low Points: Short. 9 basic levels, 4 boss levels. Difficulty is above average for a NES game, and probably too much for casual players, in fact the final boss may have many people yelling at their TV. That said, once the learning curve has passed, you'll be more comfortable with it, and the curve isn't too long. Music is catchy at first, but can get irritating over time. Lack of backgrounds is a disappointment.
If you're feeling nostalgic, pick this up, as it's a good example of a worthwhile NES game. Just be warned: it has it's flaws. Note that I listed it as hard, but games have become more difficult on average since then...