The game that launched the series stands the test of time like a true classic.
I just finished playing through it to find out, and I discovered that it's still a blast 22 years later. The NES graphics and sound hold up remarkably well; they did everything they could on the antique hardware without trying to do *too* much. If you played it back in the day, it's going to look and sound just like you remember. The controls are okay for what they are; Simon is no acrobat, but control is fairly responsive and it's easy to anticipate where your jumps will land and to time your whip strikes, once you get the hang of it.
Another thing that you'll probably remember is the punishing difficulty of many early NES-era titles. This one is no exception, but it manages to do so without feeling cheap and frustrating--for the most part. You'll die a lot, but you won't necessarily feel like the deaths were unavoidable; if you had just crouched to whip the bat (for instance), you could have made it. There are a couple of boss fights that are overly difficult, and the final stage does manage to throw in some frustration, but even that is offset by the fact that if you do make it through, you'll continue from right next to Dracula's Keep, rather than having to do it over.
All in all, if you get the chance to play this game, go for it--especially if you played it back in the day, but even if you just want to see how the series got its start. It's still a superb game, one that manages to be a heck of a lot of fun almost a quarter-century later.