You'd never heard of Super Castlevania IV until just recently? Color me genuinely surprised.

Anyway, Castlevania: Dracula X is, basically, a retelling of the PC-Engine game, Akumajō Dracula X: Chi no Rondo. It has the same basic plot, the same (quite well reproduced) soundtrack, and very similar gameplay, but the stages are all new, as are some of the bosses. It's not a port, or even a sequel, but it gets called a port a lot, and it has a bad rep for having one particularly unfair gameplay mechanic... when you get hit, there's no moment of invincibility. You can literally be bounced back and forth between enemies and die.

Outside of that issue, it plays very much like the traditional Castlevania entries (CV, CV III, etc.), in that you pretty much left to right, whipping and jumping as you cross platforms and such. There's little in the way of "Metrovania" gameplay (i.e. "Symphony of the Night" and its ilk), though there are some hidden secondary stages in spots for you to discover.

Overall, it's not a bad entry. The death bouncing is frustrating, but it doesn't ruin the game. And while it may not be quite as good as SVC IV, it is a good game with very good graphics, great music, and a tougher challenge (and not because of the death bouncing).