Difficult
If the first game was one of reactions, this game is much more of a thinking mans game. There were often times necessary hidden blocks, mandatory items for getting through certaint segments and jumps that seemed impossible on first glance. The hit detection is less leniant, making dodgin enemies incredibly difficult.
The move from 8bit sprites to 16bit ones makes the game look better and be more immersive.
Overall, a great game to master after you've beaten the first, but expect a challenge, and don't expect a completley different game.