Castlevania 3 is my favorite NES game and my second favorite Castlevania game. It perfected the series on the NES and is honestly a must-play for any gamer. It retains everything good about the first, but also has better level design, more replay value, and 3 extra characters. While these characters aren't as beautifully balanced as the Belmont Subweapons, they are balanced pretty well and offer the aforementioned replay value alongside two splitting paths. The level design is more varied as well, and it feels like a perfect blend between the action and platforming, and that includes many bosses.

Not only that, but the audiovisuals are also improved, which might sound crazy considering the excellent sound design of the first, but seriously. They made an entire sound chip and stuff, and the visuals are pushing the NES to its limits.

You should absolutely play this game. I'd recommend the Castlevania Collection, not only because of its value, but because it's the only official release of the Japanese version, which is what I played. The North American version was not only made much harder, but the sound isn't as good. Play the Japanese version.