I completed the game twice, and I'm very happy I did as the first time I got overwhelmed a bit by the difficulty but the game is actually fair as you pick all the weapons, advance and assault the enemies, I think I died maybe twice.
The game feels very, very good. The visuals are stellar, the controls are perfect and the sound effects juicy, all in a perfect NES package with all the right speeds. The ammo weapons are satisfying and the boss and half-boss fights are perfect NES ones again and they're very fun to deal with. Finally the difficulty is perfect in the end.
Great game!