The original game is a good game, but not really much more. Uprising elevated the franchise to another level.
The original game is... Let's just say that unless you're absolutely sure you can handle how punishing and unforgiving its difficulty is, I'd suggest not touching it. To put things in perspective, I'd argue that it's much harder than the original Castlevania and Mega Man.
That's for the NES version, by the way. I'm not sure if they've changed anything in the 3D Classics edition.