I've played this one before, via Nightmare in Dreamland for the GBA; a remake of this classic. I'll just start right now by saying if you have that version handy, that is the better version in my opinion just in terms of controls.

Graphically, this game is insane for being on the NES. I actually played through this because friends of ours got my wife a blanket from this and I had to replay it but on the NES.

I will say, having played it before I did not find this difficult at all, only having trouble with re-wiring my brain to the fact you press up to float rather than just multi pressing A. That took some adjustment but wasn't dealbreaking for me.

Overall, good if you don't have access to Nightmare in Dreamland; but if you do have Nightmare I wholly recommend you play that instead.